GLAST SCIENCE WRITER’S GUIDE

“Exploring the Extreme Universe”

A guide for reporters to understand the mission and purpose of the

GAMMA-RAY LARGE AREA SPACE TELESCOPE

(GLAST)

A NASA mission in collaboration with the U.S. Department of Energy

and many domestic and international partners 

 February 2008

Credit: NASA E/PO, Sonoma State University, Aurore Simonnet

National Aeronautics Space Administration

www.nasa.gov
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NASA’s Gamma-ray Large Area Space Telescope (GLAST) is a powerful 

space observatory that will:

1. Explore the most extreme environments in the Universe, where nature 

harnesses energies far beyond anything possible on Earth. 

2. Search for signs of new laws of physics and what composes the mysterious 

Dark Matter. 

3. Explain how black holes accelerate immense jets of material to nearly light 

speed. 

4. Help crack the mysteries of the stupendously powerful explosions known as 

gamma-ray bursts.

5. Answer long-standing questions across a broad range of topics, including 

solar flares, pulsars, and the origin of cosmic rays.

CREDITS

Lead Editors/Layout:

Lynn Cominsky, Sonoma State University, Calif.

Rob Gutro, NASA Goddard Space Flight Center

 (GSFC)

Robert Naeye, NASA GSFC

Layout Designer: Ruth Jennings, NASA GSFC

Contributing Authors and Editors:

J.D. (Dan) Blackwood, NASA Headquarters (HQ)

Neil Calder, U.S. Dept. of Energy (DOE), Stanford 

 Linear Accelerator Center

Neil Gehrels, NASA GSFC

Kevin Grady, NASA GSFC

Mike Greenwood, General Dynamics, AIS

F. Rick Harnden, Jr., NASA HQ 

Grey Hautaluoma, NASA HQ

Julie McEnery, NASA GSFC

Charles “Chip” Meegan, Marshall Space Flight 

 Center

Peter Michelson, Stanford University

Steve Ritz, NASA GSFC

Mark Seidleck, NASA GSFC

David Thompson, NASA GSFC

Kathy Turner, U.S. DOE

Marcus Woo, Freelance Science Writer

GLAST

(Gamma-ray Large Area Space Telescope)

SCIENCE WRITER’S GUIDE

Table of Contents

Page Topic

4...................... QUICK REFERENCE GUIDE

5...................... GLAST KEY SCIENTIFIC OBJECTIVES 

5...................... Q&A ON THE GLAST MISSION

5.................................. Mission Facts/Science

7.................................. Instruments

8.................................. Launch/Data

10................................ Partners

13.................... HISTORY OF COSMIC DISCOVERY: OPENING NEW WINDOWS

15.................... A TIMELINE OF GAMMA-RAY ASTRONOMY

17-31............... FEATURES: WHAT KINDS OF THINGS WILL GLAST STUDY?

17-18........................... FEATURE 1: ..Blazars and Active Galaxies

19-20........................... FEATURE 2: ..Gamma-ray Bursts

21-22........................... FEATURE 3: ..Neutron Stars

23................................ FEATURE 4: ..Cosmic Rays and Supernova Remnants

24................................ FEATURE 5: ..Milky Way Galaxy

24-25........................... FEATURE 6: ..The Gamma-ray Background

25-26........................... FEATURE 7: ..The Early Universe

25-26........................... FEATURE 8: ..Solar System: Sun, Moon, and Earth

28-29........................... FEATURE 9: ..Dark Matter

29-30........................... FEATURE 10: Testing Fundamental Physics

25-26........................... FEATURE 11:.Unidentified Sources and the Unknown

32....................GLAST LAUNCH AND OPERATION QUICK FACTS

33....................GLAST INSTRUMENTS

37 ...................GLAST WEB SITES

38....................ELECTROMAGNETIC SPECTRUM BASICS

39....................EDUCATION AND PUBLIC OUTREACH PRODUCTS

41....................GLAST SCIENCE GLOSSARY

46....................GLAST-RELATED ACRONYMS

Black hole-powered jet 

of electrons and other 

subatomic particles stream 

from the center of Galaxy M87 

Credit: NASA and The Hubble 

Heritage Team (STScI/AURA)

GLAST, NASA’s new gamma-ray 

observatory, will open a wide 

window on the universe. Gamma 

rays are the highest-energy form 

of light and the gamma-ray sky 

is spectacularly different from 

the one we perceive with our 

own eyes. With a huge leap in 

all key capabilities, GLAST data 

will enable scientists to answer 

persistent questions across a 

broad range of topics, including 

supermassive black-hole systems, 

pulsars, the origin of cosmic rays, 

and searches for signals of

new physics.

NASA’s GLAST mission is 

an astrophysics and particle 

physics partnership, developed 

in collaboration with the U.S. 

Department of Energy, along 

with important contributions 

from academic institutions and 

partners in France, Germany, Italy, 

Japan, Sweden, and the U.S.

TABLE OF CONTENTS
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GLAST QUICK REFERENCE GUIDE

GLAST PROJECT 

SCIENTIST:

Steve Ritz

NASA Goddard Space Flight Center

Steve.Ritz@nasa.gov

Tel. 301-286-0941

GLAST LARGE AREA 

TELESCOPE (LAT)

PRINCIPAL INVESTIGATOR:

Peter Michelson

Stanford University

peterm@stanford.edu

Tel. 650-723-3004

GLAST BURST

MONITOR (GBM)

PRINCIPAL INVESTIGATOR:

Charles “Chip” Meegan

NASA Marshall Space Flight Center

chip.meegan@nasa.gov

Tel. 256-961-7694

GLAST DEPUTY

PROJECT SCIENTIST:

Neil Gehrels

NASA Goddard Space Flight Center

Neil.Gehrels@nasa.gov

Tel. 301-286-6546

GLAST DEPUTY

PROJECT SCIENTIST:

Julie McEnery 

NASA Goddard Space Flight Center 

Julie.E.McEnery@nasa.gov

Tel. 301-286-1632

GLAST DEPUTY

PROJECT SCIENTIST:

David Thompson 

NASA Goddard Space Flight Center 

David.J.Thompson@nasa.gov

Tel. 301-286-8168

GLAST RELATED PUBLICATIONS

 • GLAST Brochure: http://glast.sonoma.edu/resources/brochure/glastbroch04.pdf

 • GLAST Fact Sheets: 

 http://glast.gsfc.nasa.gov/public/resources/pubs/factsheet/Sci_Fact_Sheet.pdf

 • http://www.fisica.uniud.it/~glast/docs/a06518glastfa1.pdf

PUBLIC AFFAIRS CONTACTS: 

NASA Headquarters

J.D. Harrington

202-358-5241

j.d.harrington@nasa.gov

Goddard Space Flight Center

Rob Gutro

301-286-4044

Robert.J.Gutro@nasa.gov

Marshall Space Flight Center

Jennifer Morcone

256-544-7199

Jennifer.J.Morcone@nasa.gov

NASA-TV

Deanna Kekesi

Television Producer

301-286-0041

Dee.Kekesi@nasa.gov

Sonoma State University

Lynn Cominsky

GLAST Press Officer

707-664-2655

lynnc@universe.sonoma.edu

U.S. Dept. of Energy, SLAC

Kelen Tuttle

650-926-2585

kelen.tuttle@slac.stanford.edu

Stanford University

Dan Stober, Science Writer

Standford News Service

650-721-6965

dstober@stanford.edu

U.S. Dept of Energy

Peter Lincoln

202-586-9010

peter.lincoln@science.doe.gov

Goddard Space Flight Center

Robert Naeye

301-286-4453

Robert.P.Naeye@nasa.gov

GLAST RELATED WEB SITES

MAIN NASA GLAST WEB SITE: http://www.nasa.gov/glast

NASA GLAST MISSION WEB SITE: http://glast.gsfc.nasa.gov

EDUCATION WEB SITE SONOMA STATE UNIVERSITY: http://glast.sonoma.edu

GLAST Multimedia Gallery: http://glast.sonoma.edu/resources

MAIN GLAST INSTRUMENT WEB SITES:

LAT instrument at Stanford University: http://glast.stanford.edu/

GBM instrument at Marshall Space Flight Center: http://www.batse.msfc.nasa.gov/gbm/

GLAST is NASA’s next-generation mission designed to explore the 

most energetic phenomena in our Universe.

GLAST KEY SCIENTIFIC OBJECTIVES 

NASA’s Gamma-ray Large Area Space Telescope (GLAST) is a powerful 

space observatory that will:

1. Explore the most extreme environments in the Universe, where nature 

harnesses energies far beyond anything possible on Earth. 

2. Search for signs of new laws of physics and what composes the mysterious 

Dark Matter. 

3. Explain how black holes accelerate immense jets of material to nearly light 

speed. 

4. Help crack the mysteries of the stupendously powerful explosions known as 

gamma-ray bursts.

5. Answer long-standing questions across a broad range of topics, including 

solar flares, pulsars, and the origin of cosmic rays.

Q&A ON THE GLAST MISSION

MISSION FACTS / SCIENCE:

WHAT DOES “GLAST” STAND FOR? Gamma-ray Large Area Space Telescope

WHAT IS THE PURPOSE OF THE GLAST MISSION? 

The Universe is home to numerous exotic and beautiful phenomena, some of which can 

generate inconceivable amounts of energy. GLAST will open this high-energy world. 

Astronomers will have a superior tool to study how black holes, notorious for pulling matter 

in, can accelerate jets of gas outward at fantastic speeds. Physicists will be able to search for 

signals of new fundamental processes that are inaccessible in ground-based accelerators and 

observatories. 

WHAT ARE GLAST’S MAIN MISSION OBJECTIVES?

•	 To understand the mechanisms of particle acceleration in active galactic nuclei (AGNs), 

neutron stars, and supernova remnants (SNRs). 

•	 Resolve the gamma-ray sky: characterize unidentified sources and diffuse emission.

•	 Determine the high-energy behavior of gamma-ray bursts (GRBs) and variable sources. 

•	 Probe dark matter and the early Universe.

WHAT KINDS OF THINGS WILL GLAST STUDY? (See Features section of this guide) 

 1. Blazars and Active Galaxies

 2. Gamma-ray Bursts

 3. Neutron Stars

 4. Cosmic Rays and Supernova Remnants

 5. Milky Way Galaxy

 6. The Gamma-ray Background 

 7. The Early Universe

 8. Solar System: Sun, Moon, and Earth

 9. Dark Matter 

10. Testing Fundamental Physics

11. Unidentified Sources and the Unknown

WHAT'S NEW AND REVOLUTIONARY ABOUT THIS MISSION?

GLAST is the first imaging gamma-ray observatory to survey the entire sky every day and with 

high sensitivity. It will give scientists a unique opportunity to learn about the ever-changing 

Q & A

QUICK REFERENCE

OBJECTIVESSCIENTIFIC
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Universe at extreme energies. GLAST will detect thousands of gamma-ray sources, most of 

which will be supermassive black holes in the cores of distant galaxies. GLAST uses Einstein’s 

principle of E = mc2 to convert gamma rays into matter in order to track their cosmic origins. 

GLAST observations may reveal signatures of new physics, including the potential to identify the 

unknown particle which may compose dark matter.

WHAT ARE SOME OF THE QUESTIONS GLAST HOPES TO ANSWER? 

How do black holes accelerate jets of material to nearly light speed? What is the mysterious 

dark matter? What mechanism produces the stupendously powerful explosions known as 

gamma-ray bursts? How do solar flares generate high-energy particles? How do pulsars work? 

What is the origin of cosmic rays? What else out there is shining gamma rays? 

WHAT ARE GAMMA RAYS? 

Gamma rays are the highest-energy forms of light in the electromagnetic spectrum. For more 

details, see the feature article on page 38. 

WHAT PREVIOUS MISSIONS DOES GLAST CONTINUE AND IMPROVE UPON? 

GLAST follows in the footsteps of NASA’s Compton Gamma-ray Observatory (CGRO) EGRET 

and BATSE instruments, which were operational between 1991 and 1999. GLAST will have a 

field of view and sky survey twice as large as that of the CGRO, and a sensitivity more than 30 

times greater than Compton’s EGRET instrument. GLAST will also improve upon the BATSE 

instrument.

WHAT’S THE DIFFERENCE BETWEEN THE SWIFT AND GLAST SATELLITES? 

Both missions look at gamma-ray bursts (GRBs), but in different ways. Swift can rapidly and 

precisely determine the locations of GRBs and observe their afterglows at X-ray, ultraviolet, and 

optical wavelengths. GLAST will provide exquisite observations of the burst over the gammaray spectrum, giving scientists their first complete view of the total energy released in these 

extraordinary events. Beyond GRB science, GLAST is a multipurpose observatory that will study 

a broad range of cosmic phenomena. Swift is also a multipurpose observatory, but was built 

primarily to study GRBs. 

HOW BIG IS THE SPACECRAFT? 

It is 9.2 feet (2.8 meters) high by 8.2 feet (2.5 meters) in diameter when stowed, where it is just 

under the 9-foot diameter allowed in the fairing. GLAST becomes a little bit taller and much 

wider after it is launched into space, when the Ku-band antenna deploys and the solar arrays 

are extended.

HOW LONG WILL THE MISSION LAST? 

GLAST is expected to operate for a minimum of five years, but has a goal to operate 10 years. 

WHERE WILL DATA ANALYSIS HAPPEN?

Around the world. Data analysis will be supported by GLAST’s international science team and 

by the mission’s science center, located at NASA’s Goddard Space Flight Center (GSFC). The 

LAT Instrument Science Operations Center (ISOC) is located at Stanford Linear Accelerator 

Center, Menlo Park, Calif. The (GBM) Instrument Operations Center is located at the National 

Space Science and Technology Center (NSSTC) in Huntsville, Ala.

WHAT DOES GLAST MEAN TO THE AVERAGE PERSON? 

The Universe looks remarkably different outside the narrow range of colors we can see with our 

eyes. GLAST’s spectacular high-energy gamma-ray “eyeglasses” will reveal hidden wonders, 

opening our minds to new possibilities and discoveries, expanding our understanding of the 

Universe and our place in it. These new perspectives help us to think differently as well as 

inspire new generations of students.

GLAST WILL STUDY THE ORIGIN OF COSMIC RAYS. HOW DO COSMIC RAYS AFFECT 

US? 

Although you may never yourself be bombarded by a primary cosmic ray (we are shielded from 

them by Earth’s atmosphere), we are bombarded all the time by the secondary cascades of 

particles that are created when cosmic rays interact with Earth’s atmosphere. These secondary 

particles are not as energetic, but they provide a constant background radiation to which we 

are all constantly exposed. Spacecraft and high-altitude planes certainly feel their effects. With 

the high energy of primary cosmic rays concentrated in such a small bundle, they can disrupt 

computer hardware or sensitive electronics and these instruments have to be shielded in 

vehicles traveling above the atmosphere. 

WHAT DOES GLAST COST TO DESIGN, BUILD AND LAUNCH?

U.S. contribution $600 million; international contribution $90 million; Total $690 million. 

WHERE IS GLAST’S ORBIT AND WHY IS GLAST IN THIS ORBIT? 

Although gamma rays can travel across the Universe to give us their information, they cannot 

penetrate even the thinnest part of Earth’s upper atmosphere. Therefore the detectors need to 

be placed above the atmosphere. To accomplish this, GLAST will be launched into circular orbit 

around Earth at an altitude of about 560 km (350 miles). This is a low-Earth orbit. This orbit is 

chosen to minimize the effects of charged particles that surround Earth, and which would create 

additional unwanted background signals in the detectors, while still ensuring the full mission 

lifetime. At that altitude, the observatory will circle Earth every 95 minutes. In sky-survey mode, 

GLAST will be able to view the entire sky in just two orbits, or about 3 hours. 

WHAT DO PROJECT SCIENTISTS DO? 

The primary role of the Project Scientist is to provide the scientific leadership necessary to 

assure that the mission implementation will meet or exceed the scientific requirements. The 

Project Scientist and her/his deputies are integral members of the Project management team. To 

accomplish these goals, the Project Scientist functions include: providing scientific oversight of 

all elements of the mission, reviewing and recommending approval or disapproval of proposed 

modifications to the science requirements or to the instruments, acting as the primary science 

interface between the science community and the project, and assuring public dissemination 

of scientific results through professional groups, peer reviewed publications, conferences, 

workshops, and the relevant public-affairs offices.

INSTRUMENTS:

WHAT ARE THE NAMES OF THE GLAST INSTRUMENTS?

1) Large Area Telescope (LAT) 

2) GLAST Burst Monitor (GBM)

WHAT DOES THE LARGE AREA TELESCOPE (LAT) DO AND HOW DOES IT WORK? 

The LAT detects gamma rays by using Einstein’s famous E = mc2 equation in a technique 

known as pair production. When a gamma ray, which is pure energy, slams into a layer of 

tungsten in the detector, it can create a pair of subatomic particles (an electron and its antimatter 

counterpart, a positron). The direction of the incoming gamma ray is determined by projecting 

the direction of these particles back to their source using several layers of high-precision silicon 

tracking detectors. A separate detector, called a calorimeter, absorbs and measures the energy 

of the particles. Since the energy of the particles created depends on the energy of the original 

gamma ray, counting up the total energy determines the energy of that gamma ray. Because 

the LAT in orbit is bombarded by many more particles than gamma rays, it wears a “hat” – a 

third detector that produces a signal when a particle, but not a gamma ray, goes through it. The 

combination of no signal in this outer detector (“the dog that did not bark”), plus an electronpositron pair of tracks created inside the LAT, signals a gamma ray. Working one gamma ray at 

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WHEN ARE THE FIRST RESULTS EXPECTED? 

The observatory is activated and tested in the first 60 days after launch. Basic “first light” results 

may come by day 90. 

WHAT WILL THE GLAST IMAGES LOOK LIKE? 

GLAST images will typically be intensity gamma-ray maps, often with different colors 

representing different energy ranges. These maps will be either a small number of individual 

sources, or as much as the entire sky. There will also be information about energy spectra and 

timing in some cases. An example of a simulated GLAST sky is shown below.

HOW WILL THE DATA BE DISTRIBUTED?

The data will be made available over the Internet from the GLAST Science Support Center 

(GSSC) at NASA’s Goddard Space Flight Center. 

HOW AND WHERE WILL THE DATA BE PROCESSED?

Data analysis will be performed at two remote science centers, located at the Stanford Linear 

Accelerator Center, operated by Stanford University for the U.S. Dept. of Energy, and at NASA’s 

Marshall Space Flight Center, in Huntsville, Alabama. GLAST data goes to the GSSC and is 

then distributed to the science community. 

WHERE WILL MISSION OPERATIONS BE? 

Mission operations will be performed from facilities at NASA’s Goddard Space Flight Center. 

WILL THE GLAST MISSION BE RENAMED AFTER LAUNCH?

Yes. GLAST will receive a new name once it is in orbit.

WHO CAN HELP WITH PRESS RELEASES, INTERVIEWS, OTHER RESOURCES? VIDEO? 

NASA and Sonoma State public-affairs officers can provide the latest press releases, breaking 

news, video, and arrange interviews. At Sonoma State University, contact Lynn Cominsky, 

Education and Public Outreach, Tel. 707-664-2655, email: lynnc@universe.sonoma.edu. 

a time, the LAT will make gamma-ray images of astronomical objects, while also determining the 

energy for each detected gamma ray. For more detail on the LAT, see page 34.

WHO HELPED CREATE THE LAT?

The U.S. Department of Energy (DOE) and NASA partnered on the 

building of the Large Area Telescope (LAT), the primary instrument on 

GLAST. There were major contributions from France, Italy, Japan, and 

Sweden. The laboratory that managed the construction of the LAT is the 

Stanford Linear Accelerator Center, a DOE-funded lab, located at and 

managed by Stanford University. Although the LAT is the work of literally 

hundreds of scientists, engineers, and technicians, the individual who 

contributed the most to the original design is Bill Atwood, now at the 

University of California, Santa Cruz.

WHERE WAS THE LAT TESTED? 

The LAT was tested extensively during the summer of 2006 at the U.S. 

Naval Research Laboratory in Washington, D.C. LAT hardware was also 

used in beam tests at the European Center for Nuclear Research (CERN) 

and the German Heavy Ion Facility (GSI). The LAT was shipped to the 

General Dynamics facility in Arizona for integration onto the spacecraft 

bus. The General Dynamics spacecraft bus provides the power, data, and 

pointing resources that will enable the LAT to perform its survey of the 

Universe. Subsequent to the mechanical integration, the command, data, 

and power interfaces between the instrument and the spacecraft were 

tested rigorously to insure the compatibility of this spaceflight hardware 

that had been manufactured all around the globe.

 

WHAT DOES THE GLAST BURST MONITOR (GBM) DO? 

The GLAST Burst Monitor (GBM) was selected as a complementary instrument for the GLAST 

mission and will be sensitive to X rays and gamma rays with energies between 8 keV and 30 

MeV.

WHO HELPED CREATE THE GBM?

The development of the GLAST Burst Monitor and analysis of its observational data is a 

collaborative effort between the National Space Science and Technology Center in the U.S. and 

the Max Planck Institute for Extraterrestrial Physics (MPE) in Germany.

HOW WILL THE INSTRUMENTS WORK TOGETHER?

The GBM has an even larger field of view than the LAT. The GBM can see all directions at once, 

except for the area where Earth blocks its view. When the GBM detects a bright gamma-ray 

burst, it immediately sends a signal to the LAT to observe that area of the sky. It will do this if it is 

not already in the field of view, and if it is permissible to move there due to logistical constraints. 

WHAT’S A “GEE-WHIZ FACT” ABOUT THE TECHNOLOGY? 

The LAT is a 3-ton detector with almost a million channels of electronics, but it uses less than 

half the power of an ordinary hair dryer.

LAUNCH / DATA:

WHERE AND WHEN IS THE LAUNCH SCHEDULED? 

The launch is scheduled for early 2008 from Cape Canaveral Air Station, on Florida’s east coast. 

GLAST will be carried on a Delta II Heavy launch vehicle, with 9 solid rocket boosters. The 

solids are actually from the Delta III series (hence the term “heavy”), mounted on a Delta II. It 

has a 10 foot fairing and two stages.

Q & A

Q & A

One of the Large 

Area Telescope 

towers, which is 

composed of a 

stack of interleaved 

planes of silicon 

strips and tungsten 

converters. The 

LAT has 16 of these 

towers in a 4x4 

array.

Credit: NASA

Simulated GLAST Sky after one year of operation. 

Credit: LAT Team
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At NASA’s Goddard Space Flight Center, contact: Rob Gutro, Public Affairs Officer, Tel. 

301-286-4044 or by email Robert.J.Gutro@nasa.gov or Robert Naeye, Science Writer, Tel. 

301-286-4453, Robert.P.Naeye@nasa.gov. Video and animation requests should be directed to 

Deanna Kekesi at NASA-TV, Tel. 301-286-0041, Dee.Kekesi@nasa.gov.

WHO CAN HELP WITH LAUNCH SUPPORT IN PUBLIC AFFAIRS? 

George Diller will provide public-affairs launch support from Kennedy Space Center, Fla. Tel. 

321-861-7643 Email: george.h.diller@nasa.gov. The GLAST launch will occur from Cape 

Canaveral Air Station, adjacent to the Kennedy Space Center.

PARTNERS: 

WHO ARE THE PARTNERS INVOLVED WITH THE MISSION? 

NASA’s GLAST mission is an astrophysics and particle-physics partnership, developed in 

collaboration with the U.S. Department of Energy, along with important contributions from 

academic institutions and partners in France, Germany, Italy, Japan, Sweden, and the U.S.

PARTNERS ON GLAST HARDWARE INCLUDE: 

• French Institutions

 Centre d’Études nucléaires de Bordeaux Gradignan (IN2P3/CENBG)

 Commissariat à l’Energie Atomique, Département d’Astrophysique (CEA/DAPNIA), de 

 physique des Particules, de physique Nucléaire et de l’Instrumentation Associée, CEA, 

 Saclay

 Institut National de Physique Nucléaire et de Physique des Particules, IN2P3

 Laboratoire de Physique Théorique et Astroparticules, Montpellier, GAM (IN2P3/LPTA)

 Laboratoire Leprince-Ringuet de l’École Polytechnique (IN2P3/LLR)

• German Institution

 Max Planck Institute for Extraterrestrial Physics

• Italian Institutions

 Instituto Nazionale di Fisica Nucleare

 Italian Space Agency (ASI)

 Istituto di Fisica Cosmica, Milano, CNR

 INFN and University of Bari

 INFN and University of Padova

 INFN and University of Perugia

 INFN and University of Pisa

 INFN and University of Rome 2

 INFN and University of Trieste

 INFN and University of Udine

• Japanese Institutions 

 University of Tokyo

 Tokyo Institute of Technology

 Institute for Cosmic-Ray Research (ICRR)

 Institute for Space and Astronautical Science (ISAS)

 Hiroshima University

• Swedish Institutions

 Royal Institute of Technology (KTH)

 Stockholms Universitet 

• U.S. Institutions

 Los Alamos National Laboratory

 NASA’s Goddard Space Flight Center, Astrophysics Science Division

 NASA’s Marshall Space Flight Center

 Ohio State University, Physics Department 

 Sonoma State University, NASA’s Education and Public Outreach Group

 Stanford University (SU), Physics Department

 Stanford University, Hansen Experimental Physics Laboratory (HEPL) and Kavli Institute 

 for Particle Astrophysics and Cosmology (KIPAC)

 Stanford University, Stanford Linear Accelerator Center (SLAC)

 Texas A&M University-Kingsville

 University of Alabama in Huntsville

 University of California at Santa Cruz, Physics Department & SCIPP

 University of Washington

 U.S. Department of Energy

 U.S. Naval Research Laboratory, High Energy Space Environment (HESE) branch 

WHAT WERE THE HARDWARE CONTRIBUTIONS OF THE FRENCH PARTNERS? 

They designed and built the support structure for the LAT Calorimeter. 

WHAT WERE THE HARDWARE CONTRIBUTIONS OF THE GERMAN PARTNER?

The Max Planck Institute built all of the sensors and the power-supply box and support on 

the GLAST Burst Monitor (GBM) instrument. One of its scientists is the GBM Co-principal 

Investigator.

WHAT WERE THE HARDWARE CONTRIBUTIONS OF THE ITALIAN PARTNERS?

They provided particle physics and astrophysics expertise and physically built the LAT Tracker. 

WHAT WERE THE HARDWARE CONTRIBUTIONS OF THE JAPANESE PARTNERS?

They provided oversight in the making of the silicon-strip detectors in the LAT Tracker. 

WHAT WERE THE HARDWARE CONTRIBUTIONS OF THE SWEDISH PARTNERS?

They provided sensors for the LAT Calorimeter.

WHAT WERE THE HARDWARE CONTRIBUTIONS OF NASA’s GODDARD SPACE FLIGHT 

CENTER?

NASA Goddard managed and built the LAT Anticoincidence Detector (ACD). The overall GLAST 

Program Mission Management and Mission Systems Engineering are provided by NASA 

Goddard. In addition, the Mission Operations Center (MOC) and the GLAST Science Support 

Center (GSSC) were provided by and are located at NASA Goddard.

WHAT WERE THE CONTRIBUTIONS OF NASA’s KENNEDY SPACE CENTER?

NASA’s Launch Services Program office at the Kennedy Space Center (KSC) is responsible 

for countdown management of the Delta II rocket for GLAST. KSC is also responsible for the 

integration of GLAST with the Delta II, provides ground support necessary for final GLAST 

spacecraft preparations. The Delta II is provided to NASA as a launch service by the United 

Launch Alliance. The spacecraft will launch from Space Launch Complex 17 at Cape Canaveral 

Air Force Station.

WHAT WERE THE CONTRIBUTIONS OF NASA’s MARSHALL SPACE FLIGHT CENTER?

It provided the Data Processing Unit and instrument integration and testing. The management 

of the GLAST Burst Monitor (GBM) instrument is done through the National Space Science and 

Technical Center, out of NASA Marshall, Huntsville, Ala. Charles Meegan is the GBM Principal 

Investigator.

WHAT WERE THE HARDWARE CONTRIBUTIONS OF THE NAVAL RESEARCH 

LABORATORY?

It managed the building of the LAT Calorimeter. 

WHAT WERE THE HARDWARE CONTRIBUTIONS OF THE OHIO STATE UNIVERSITY?

It provided particle physicists, and helped with trigger and data systems, including the algorithms 

on-board.

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WHAT WERE THE CONTRIBUTIONS OF SONOMA STATE UNIVERSITY?

It provides management of education and public outreach.

WHAT WERE THE HARDWARE CONTRIBUTIONS OF STANFORD UNIVERSITY?

It is the lead on the Large Area Telescope (LAT). Peter Michelson is the LAT Principal 

Investigator. Stanford managed the LAT and hosts the Instrument Science Operations Center 

(ISOC) at the Stanford Linear Accelerator Center. The ISOC is where all the raw data from the 

LAT is processed and made ready for scientific analysis. The data is sent to the GLAST Science 

Support Center at NASA GSFC from where it is distributed to the scientific community.

WHAT WERE THE CONTRIBUTIONS OF THE UNIVERSITY OF CALIFORNIA, SANTA 

CRUZ?

It provided management of the Tracker in the LAT. 

WHAT WERE THE CONTRIBUTIONS OF THE UNIVERSITY OF WASHINGTON?

It provided software support.

WHAT WERE THE U.S. DEPARTMENT OF ENERGY’S (DOE) AND SLAC’S HARDWARE 

CONTRIBUTIONS?

The Large Area Telescope (LAT) is managed at the U.S. DOE Stanford Linear Accelerator 

Center (SLAC), a U.S. DOE lab. SLAC was responsible for the overall design and development 

of the LAT.

WHO IS RESPONSIBLE FOR BUILDING THE ACTUAL SPACECRAFT? 

General Dynamics Advanced Information Systems, Gilbert, Arizona. 

WHAT DOES THE SCIENTIFIC COMMUNITY THINK OF THE GLAST MISSION?

The National Academies of Sciences ranked GLAST as the top-priority mid-sized project in its 

2000 Decadal Survey of Astronomy and Astrophysics.

HISTORY OF COSMIC DISCOVERY: OPENING NEW WINDOWS

By Robert Naeye

An old saying goes: Those who don’t remember the past are condemned to repeat it. But 

research astronomers are quite content to repeat the history of their field, and for good reason. 

If there’s one theme that has played itself out over and over in astronomy, it’s the fact that 

whenever scientists open a new window on our Universe, or bring about a major upgrade in 

instrumentation, a period of remarkable discoveries is bound to follow. We can expect the same 

for GLAST.

A case in point dates back to dawn of the telescopic era. Although the telescope was invented 

in Holland, the great Italian Renaissance scientist Galileo Galilei was the first to systematically 

train this newfangled device on the heavens. In a short period of time starting in 1609, he 

revolutionized human understanding of our Universe. He discovered the four largest moons of 

Jupiter and the phases of Venus, which bolstered the Copernican view of a Sun-centered solar 

system. Galileo saw sunspots, mountains on the Moon, and the rings of Saturn. With just a tiny, 

crude telescope he resolved the Milky Way into “congeries of innumerable stars distributed in 

clusters.”

As astronomers built bigger and better telescopes 

during the 17th, 18th, and 19th centuries, they discovered 

new planets (Uranus and Neptune), new moons, 

asteroids, and entirely new classes of objects, 

including star-forming nebulae, planetary nebulae, 

“spiral nebulae,” and binary stars. With improved 

optics, astronomers of the mid-1800s used the parallax 

method to make the first accurate measurements of 

the distances to other stars, proving that other celestial 

objects lie at immense distances from Earth. The 

development of spectroscopes in the late 19th century 

began to reveal the composition of stars.

In the early 20th century, researchers developed a 

powerful one-two combination: photographic film 

coupled to the first truly large telescopes. Both 

advances enabled astronomers to see much fainter and deeper objects than ever before. In 

1923-24, Edwin Hubble used the 100-inch telescope on California’s Mount Wilson to prove that 

spiral nebulae were actually “island universes” — external galaxies unto themselves. Just five 

years later, Hubble discovered that our Universe is expanding, laying the foundations of modern 

Big Bang cosmology.

Arguably the most profound achievement of the 20th century, however, was the opening up of 

the entire electromagnetic spectrum, some of which is accessible only from space. Discoveries 

in radio, X-ray, and gamma-ray astronomy shattered the illusions of a sedate, slowly changing 

cosmos. We live in a Universe of explosions, collisions, and processes involving mind-boggling 

temperatures and energies that would have been incomprehensible to the astronomers of 

yesteryear. 

Following in the footsteps of the pioneering work of Karl Jansky and Grote Reber in the 1930s 

and 40s, astronomers came to realize that the radio sky contained a wealth of information about 

the solar system, stars, galaxies, and even more exotic objects. Thanks to the opening of the 

radio window, astronomers discovered quasars, pulsars, the cosmic microwave background, the 

spiral structure of our Milky Way, dark matter, and incredible jets shooting away from the centers 

of large galaxies. NASA’s missions such as COBE and WMAP have bolstered leading theories 

about the origin and possible future of our Universe.

Galileo Galilei (1564-1642). 

Credit: ESA

HISTORY

Q & A

General Dynamics clean room, standing are: Chip Meegan, NASA Marshall 

Space Flight Center, Hunstville, Ala.; Peter Michelson, Stanford University, 

Stanford, Calif.; Steve Ritz, from NASA Goddard Space Flight Center, 

Greenbelt, Md. Kneeling are: Bill Atwood, University of California at 

Santa Cruz, Calif.; Dan Blackwood, NASA Headquarters; Rick Harnden, 

NASA Headquarters, Washington; and Neil Johnson, Naval Research 

Laboratory, Washington. In the right corner, a technician checks the satellite. 

Credit: NASA and General Dynamics
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In 1962, Riccardo Giacconi and several colleagues opened up yet another window when they 

launched a sounding rocket above the atmosphere. An X-ray detector picked up the powerful 

source Scorpius X-1 and a diffuse background glow of X rays. Subsequent balloon and rocket 

experiments, followed by satellites such as Uhuru, Einstein, ROSAT, Chandra, XMM-Newton, 

and Suzaku, have studied black holes, supernovae, relativistic jets, and active galaxies. For 

pioneering a new branch of astrophysics, Giacconi was honored with the 2002 Nobel Prize for 

Physics.

Also toward the end of the 20th century, scientists opened up the gamma-ray window, eventually 

leading to the discovery of gamma-ray bursts, gamma-ray blazars, cosmic-ray interactions, 

and other phenomena. Infrared astronomy is penetrating star-forming regions and yielding 

information about extrasolar planets and the disks that give birth to planets.

In recent times, the advent of precision spectrometers has 

enabled the discovery of more than 200 extrasolar planets. 

CCDs coupled to the new generation of 8- to 10-meter 

telescopes, and orbiting observatories such as the Hubble 

Space Telescope, are seeing back to an epoch when our 

Universe was just 1 billion years old. By catching supernovae 

in distant galaxies, these observatories have shown that our 

Universe’s expansion is accelerating.

Various orbiting and ground-based observatories have 

opened up almost the entire electromagnetic spectrum, with 

unexpected discoveries coming with almost every step. But the 

gamma-ray spectrum from 10 to 100 gigaelectronvolts (GeV) is 

virtually unexplored. GLAST’s primary science instrument, the 

Large Area Telescope (LAT), will fill in that gap. The EGRET 

instrument on NASA’s Compton Gamma-ray Observatory 

saw hints of interesting and unexpected phenomena in that high-energy range, but GLAST 

will provide our first detailed look at that window. Expect a wealth of discoveries, and some big 

surprises, from GLAST!

A TIMELINE OF GAMMA-RAY ASTRONOMY

By Robert Naeye and David Thompson

1950s Physicist Philip Morrison and others predict that cosmic rays interacting with 

interstellar material will produce gamma-ray emission from our galaxy.

Early 1960s The first balloon experiments, and NASA’s Explorer 11 satellite, detect the first 

hints of 100 MeV gamma-ray emission from our galaxy, but the results are inconclusive. The 

lack of an easily detectable signal shows that the 1950’s predictions were overly optimistic.

Early 1960s The first generation of ground-based Atmospheric Cherenkov Telescopes (ACTs) 

become operational in the U.S. and U.S.S.R. ACTs detect blue Cherenkov light created when 

very-high-energy (hard) gamma rays from space interact with molecules in Earth’s atmosphere. 

The early ACTs yield inconclusive results, with no definitive detections. 

Late 1960s U.S. military Vela satellites serendipitously detect gamma-ray bursts (GRBs) while 

looking for clandestine Soviet nuclear tests. But the existence of GRBs remains classified until 

1973.

1967-1969 NASA’s Orbiting Solar Observatory (OSO-3) detects a grand total of 621 gammaray photons from deep space, representing a major breakthrough. It verifies the existence 

of galactic emission from cosmic-ray interactions, and discovers the diffuse gamma-ray 

background. OSO-3 results are quickly confirmed by balloon experiments. 

Early 1970s Gamma-ray detectors on the command modules for Apollo 15 and 16, while en 

route to the Moon, discover a diffuse background of low-energy gamma rays. These same 

instruments helped map gamma rays emitted from radioactive elements on the lunar surface.

1972 NASA’s Small Astronomy Satellite-2 (SAS-2) confirms the diffuse gamma-ray 

background discovered by OSO-3. SAS-2 shows that the galactic emission is related to the 

structure of the Milky Way, it studies the Crab and Vela gamma-ray pulsars, and finds an 

unexpected point source, which later turns out to be the neutron star Geminga.

1975-1981 The European COS-B satellite, which is similar to SAS-2 in size and cost, 

discovers 25 additional gamma-ray point sources, some of which remain unidentified. Others 

turn out to be pulsars. Another one of the objects is the first extragalactic gamma-ray source: 3C 

273, which is a relatively nearby quasar. It also detects diffuse galactic emission.

1979-1981 NASA’S High-Energy Astrophysics Observatory-3 (HEAO-3) discovers lowenergy (soft) gamma rays coming from the galactic center from the annihilation of electrons and 

positrons. (This is the 511 keV line, which some scientists consider to be hard X rays.) Some 

still-unknown process must be producing antimatter in the region around the galactic center. 

1980-1989 NASA’s Solar Maximum Mission detects soft gamma rays from solar flares.

Late 1980s The second generation of ACTs becomes operational, led by the 10-meter Whipple 

Telescope in Arizona. Whipple indirectly detects hard gamma rays from the direction of the Crab 

Nebula, but not the pulsar at the center of the nebula.

Late 1980s Balloon experiments detect gamma rays from radioactive elements produced by 

Supernova 1987A, proving that supernovae produce new elements as predicted by theory.

Late 1980s NASA and the U.S.S.R. fly several dedicated missions to study GRBs, increasing 

the number of bursts and the number of theories about their origins.

NASA’s Compton Gamma-ray 

Observatory being deployed by 

the Space Shuttle in 1991. 

Credit: NASA

T I M E L I N E 

HISTORY

Credit: Sonoma State University/Aurore Simonet
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1991-2000 The Compton Gamma-ray Observatory (CGRO), one of NASA’s four Great 

Observatories, revolutionizes gamma-ray astronomy with a series of major discoveries. 

Designed for two years of operation, CGRO returns data for nine years, and is de-orbited 

because of a gyro-hardware failure. The BATSE instrument detects more than 2,700 GRBs and 

shows that they come from all over the sky, strongly suggesting they are explosions occurring 

in distant galaxies. It also shows that GRBs seem to occur in two types: long (greater than two 

seconds) and short (less than two seconds). The EGRET instrument finds 271 point sources, 

including about 70 blazars and six pulsars, but two-thirds of the sources remain unidentified. 

The discovery of so many blazars was unexpected. The COMPTEL instrument maps the 

galactic distribution of aluminum-26, showing where stars are forming in the Milky Way. The 

OSSE instrument maps the annihilation line from the galactic center more accurately, and finds 

gamma-ray emission from X-ray binaries and Seyfert galaxies.

Early 1990s Ground-based ACTs discover hard gamma rays from several blazars. To the 

amazement of astronomers, this emission varies on a timescale of just minutes to hours.

1997-2003 The Italian-Dutch BeppoSAX satellite, though mainly used to study X rays, 

localizes several GRB positions quickly through observations of the afterglows of long GRBs. 

The positions are precise enough that follow-up ground-based observations, and later 

observations from the Hubble Space Telescope, prove that the bursts occur at great distances, 

a major breakthrough.

2000-2007 NASA’s High-Energy Transient (HETE-2) satellite helps firm up the connection 

between long GRBs and supernovae.

2002-present NASA’s Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) 

satellite continues to advance astronomers’ understanding of how particles are accelerated and 

how energy is released in solar flares. RHESSI serendipitously detects polarization in a GRB, 

showing that powerful magnetic fields must be involved.

2002-present Among many other studies, the European Space Agency’s International 

Gamma-Ray Astrophysics Laboratory (INTEGRAL) satellite measures aluminum-26 levels 

throughout our galaxy, demonstrating that the Milky Way produces, on average, about two 

supernovae per century.

2004-present NASA’s Swift satellite is currently detecting about 100 GRBs per year, and 

localizing many of them for follow-up studies. The mission is showing that GRBs are more 

diverse than expected, and have a variety of origins. The follow-up of short GRB afterglows 

lends strong support to the theory that some of these events come from neutron star-neutron 

star mergers, or black hole-neutron star mergers.

2000s A new generation of advanced ground-based ACTs is providing unprecedented 

sensitivity and resolution in very-high-energy gamma-ray astronomy. Led by the European 

High Energy Stereoscopy System (H.E.S.S.), an array of four telescopes in Namibia, these 

detectors are finding pulsar-wind nebulae, binary systems, supernova remnants, and many 

unidentified sources. Other important ACTs include CANGAROO (an Australian-Japanese 

facility based in Australia), MAGIC (located on La Palma in the Canary Islands), and VERITAS 

(based in Arizona). MILAGRO (based in New Mexico) is using a large swimming pool full 

of photomultiplier tubes to conduct a survey of the gamma-ray sky. These ground-based 

experiments complement GLAST by extending detections to the highest gamma-ray energies.

2007 The Italian satellite AGILE launches on April 23. It has a high-energy gamma-ray 

detector with a sensitivity similar to EGRET’s, but with a wider field of view.

2008 Launch of NASA’s Gamma-ray Large Area Space Telescope (GLAST). 

FEATURES: WHAT KINDS OF THINGS WILL GLAST STUDY?

Following are a list of things that GLAST will study, followed by a feature explaining each one, 

and how GLAST will explore it.

1. Blazars and Active Galaxies

2. Gamma-ray Bursts

3. Neutron Stars

4. Cosmic Rays and Supernova Remnants

5. Milky Way Galaxy

6. The Gamma-ray Background 

7. The Early Universe

8. Solar System: Sun, Moon, and Earth

9. Dark Matter 

10. Testing Fundamental Physics

11. Unidentified Sources and the Unknown

1. Blazars and Active Galaxies

By Robert Naeye

GLAST will study a wide variety of astronomical objects and phenomena, but according to 

GLAST Project Scientist Steve Ritz of NASA’s Goddard Space Flight Center in Greenbelt, Md., 

“Active galactic nuclei will be GLAST’s bread and butter. There are guaranteed results.”

Active galactic nuclei, or AGN for short, are galaxies with extraordinarily luminous cores 

powered by black holes containing millions or even billions of times more material than our 

Sun. As gas is trapped by a monster black hole’s gravity, it settles into an accretion disk and 

starts to spiral down the Universe’s ultimate drain. Before the gas crosses the black hole’s outer 

boundary (the event horizon) — beyond which nothing can escape — the material generates a 

vast outpouring of electromagnetic radiation. In the most luminous AGN, the visible light exceeds 

the combined output of an entire galaxy’s worth of stars, even though the light-emitting area is 

only about the size of our solar system.

Even more amazing, radio, optical, and X-ray telescopes have resolved jets shooting away from 

galactic cores in opposite directions. The material in these jets can rip across space at more 

than 99% the speed of light, and some jets remain tightly collimated for hundreds of thousands 

of light-years. When a jet points almost directly toward Earth, the material can appear to be 

moving faster than the speed of light. This superluminal motion is an illusion caused by the 

TIMELINE

geometry of a source moving at high speed that is nearly but not perfectly head-on. 

FEATURES

Image of the GLAST Satellite 

Credit: NASA and Sonoma State University, Aurore Simonnet
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But despite the staggering scale and speed of these jets, astronomers haven’t been able to 

answer the most basic questions about them, such as how matter is accelerated to within 

a whisker of the speed of light. “We don’t know what the jets are made of or how they are 

produced. It is one of the biggest unsolved mysteries of astrophysics. But jets are the link 

between the activity of the supermassive black hole and the AGN’s surrounding environment 

in intergalactic space,” says Peter Michelson of Stanford University in California, who is the 

Principal Investigator of GLAST’s primary science instrument: the Large Area Telescope (LAT).

The LAT will probably detect gamma rays from different types of AGN, such as radio galaxies, 

Seyfert galaxies, quasars, and blazars. But the biggest contribution may come from blazars, 

which are thought to be AGN whose black holes aim their jets almost directly at Earth. Whereas 

the Energetic Gamma-Ray Experiment Telescope (EGRET) on NASA’s Compton Gamma-ray 

Observatory identified 66 blazars during the mission, GLAST should see thousands. By studying 

the energy spectra and variability of gamma rays and other wavelengths of light coming from 

blazars, the LAT instrument should be able to determine the composition of the jets, establishing 

whether they are dominated by electrons and positrons (the antimatter counterpart of electrons), 

or by protons.

“When GLAST detects 

a blazar, it is monitoring 

violent activity from a 

black hole taking place 

in the distant past,” says 

GLAST Interdisciplinary 

Scientist Charles 

Dermer of the Naval 

Research Laboratory 

in Washington, D.C. 

“Understanding gamma 

rays from these sources 

is a form of black hole 

archeology that reveals 

the high-energy history 

of our Universe.”

The LAT may also detect AGN that do not produce jets, or whose jets are not aimed directly 

at Earth. EGRET saw hints of gamma rays from at least two radio galaxies. The High Energy 

Stereoscopic System (H.E.S.S.), an array of four telescopes currently operating in Namibia, has 

discovered that gamma rays are coming from the giant elliptical galaxy M87, whose jets do not 

point toward Earth. These gamma-ray photons may originate from a region of the accretion disk 

very near the central black hole. By observing these and other galaxies, the LAT should provide 

precious insights into the mechanism that powers AGN activity. 

Moreover, the LAT will investigate a curious discrepancy between EGRET and results from 

several ground-based observatories, including the Whipple Observatory in Arizona. EGRET 

detected low-energy gamma rays from blazars, whereas Whipple has discovered high-energy 

TeV-level gamma rays. “Ground- and space-based telescopes have detected blazars, but there 

is almost no overlap in the blazars they detect,” notes GLAST Deputy Project Scientist Julie 

McEnery of NASA’s Goddard. “Clearly, each type of telescope is seeing a different type of 

object.”

With its ability to survey the entire sky every three hours, the LAT will undoubtedly catch 

many AGN giving off giant flares of energy, and this flaring is one of the most important tools 

for studying AGN. Blazars in particular are extremely variable at all wavelengths, changing 

both their total energy output and spectra on timescales ranging from less than an hour to 

many years. The relationship of variability at different wavelengths is a crucial test for models 

attempting to explain these outbursts and to identify the nature of the jet particles. Obtaining 

measurements across the spectrum is challenging, especially on short timescales, so GLAST 

team members will communicate with other astronomers, who can point various ground- and 

space-based telescopes at flaring blazars.

2. Gamma-ray Bursts

By Robert Naeye

Gamma-ray bursts (GRBs) were discovered by American surveillance satellites in the late 

1960s. These satellites were looking for gamma rays coming from possible clandestine Soviet 

nuclear tests, but instead found brief but intense flashes of gamma rays coming from random 

directions in space.

To this day GRBs remain one of the greatest mysteries of modern astronomy. Despite lasting 

only a few milliseconds to several minutes, they are the brightest gamma-ray phenomena 

known, outshining all other sources of gamma rays combined. “An individual GRB can release in 

a matter of seconds the same amount of energy that our Sun will radiate over its 10-billion-year 

lifetime,” says GLAST Deputy Project Scientist Neil Gehrels of NASA’s Goddard Space Flight 

Center in Greenbelt, Md.

Astronomers have made considerable strides in recent years in understanding GRBs, progress 

that can be directly attributed to a series of spectacularly successful space missions. The Burst 

and Transient Source Experiment (BATSE) on NASA’s Compton Gamma-ray Observatory 

detected several thousand GRBs, and showed that they come from random directions on 

the sky — which strongly suggested that they are not of galactic origin and must occur at 

great distances. In the late 1990s, the Italian/Dutch BeppoSAX satellite was able to pinpoint 

the location of several GRBs, which enabled X-ray, optical, and radio telescopes to monitor 

their afterglows. This was a crucial development, since it enabled astronomers for the first 

time to measure distances to bursts and observe how they interacted with their surrounding 

environments. The now-defunct HETE-2 satellite and the currently operating NASA Swift 

satellite have significantly extended and 

improved these capabilities, and have lofted 

our study of GRBs to new heights.

Thanks to these missions, astronomers 

now think that most GRBs, those lasting 2 

seconds or longer (known as long GRBs), 

are associated with the explosive deaths of 

massive stars. As the star’s core collapses 

at the end of its life, it forms a black hole or 

neutron star. Computer simulations show 

that infalling stellar gas can tap the rotational 

energy of a rapidly spinning core, and 

magnetic fields can channel that material into 

two jets traveling at nearly the speed of light. 

These jets punch their way out of the dying 

star along its rotation axis. The gamma rays 

are produced by shock waves created either 

from material colliding within the jet, or from 

the jet slamming into surrounding material.

GRBs lasting less than 2 seconds (short GRBs) may originate from a variety of processes. 

Perhaps most are produced by the merger of two neutron stars, or the merger of a black hole 

and a neutron star. But others may be triggered by the collapse of the core of a massive star into 

FEATURES

FEATURES

In this radio image, two jets shoot out of the center of active galaxy 

Cygnus A. GLAST may solve the mystery of how these jets are 

produced and what they are made of. 

Credit: NRAO

Some gamma-ray bursts may result from a 

collision between two neutron stars or a black 

hole and a neutron star. This illustration depicts 

the turbulent aftermath of such a collision. 

Credit: Dana Berry / NASA
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a black hole, the collapse of a neutron star into a black hole, and powerful flares from magnetars 

(highly magnetized neutron stars). 

But despite the new revelations from Swift and other missions, many crucial questions remain 

unanswered. What types of stars die as GRBs? What is the composition of the jets? How are 

the gamma rays in the initial burst produced? What is the total energy budget of a GRB? How 

does the central engine work? How wide are the jet opening angles? How do the jets interact 

with other material to produce the gamma rays? Swift has actually complicated the picture by 

showing that GRBs are much more diverse in their properties than astronomers had imagined 

prior to the spacecraft’s launch in November 2004. As the saying goes, “If you’ve seen one 

GRB, you’ve seen one GRB.” In fact, some GRBs don’t seem to fall into either the long or short 

category and the origin of these “hybrid bursts” remains shrouded in mystery.

“GLAST is a multipurpose observatory designed to study many phenomena besides gamma-ray 

bursts, but it promises to greatly extend our knowledge of these incredibly powerful explosions,” 

says Peter Michelson of Stanford University, who is the Principal Investigator of GLAST’s Large 

Area Telescope (LAT). 

The GLAST team specifically built the other science instrument, the GLAST Burst Monitor 

(GBM), to address this mystery. “The GBM will detect approximately 200 GRBs per year,” says 

GBM Principal Investigator Charles “Chip” Meegan of NASA’s Marshall Space Flight Center in 

Huntsville, Alabama. “It’s amazing that gamma-ray bursts are so powerful that a small detector 

you could hold in one hand can observe them from distances of billions of light-years.”

The GBM and the LAT will work in tandem to attack the problem of GRBs. If the GBM picks 

up an interesting GRB in a part of the sky that is not in the LAT’s field of view at that moment, 

the spacecraft will slew autonomously so the LAT can study the burst in more detail. The GBM 

will pick up X rays and gamma rays with energies ranging from 8 keV to 30 MeV. The LAT can 

pick up gamma rays ranging from 20 MeV to 300 GeV. Former GBM Co-principal Investigator 

Giselher Lichti of the Max Planck Institute for Extraterrestrial Physics, which built the GBM 

detectors, notes that the GBM and the LAT together cover an energy range extending from 

about 10 keV to 300 GeV. “That’s seven orders of magnitude in energy coverage for GRBs,” 

he notes. “That exceeds the energy range covered by Swift enormously, thus yielding a wealth 

of new information about GRBs.” The seven orders of magnitude in energy corresponds to 23 

octaves on the musical scale, or the equivalent of four full-size piano keyboards side by side.

The LAT’s high-energy coverage will give astronomers precious insight into an energy realm that 

so far has been poorly studied. The Compton Gamma-ray Observatory’s Energetic Gamma-Ray 

Experiment Telescope (EGRET) instrument detected a handful of extremely high-energy gamma 

rays from a few GRBs. These photons did not seem to behave the same way as those detected 

at lower energies by the spacecraft’s BATSE instrument. Strangely, one of the highest-energy 

gamma rays arrived at EGRET 90 minutes later than lower-energy gamma rays arrived at 

BATSE. What causes this delayed emission? GLAST’s observations may tell the tale. “We don’t 

understand the very-high-energy range very well; it’s bizarre,” says GLAST Project Scientist 

Steve Ritz of NASA’s Goddard. “That energy range will tell us about the GRB’s central engine, 

so the LAT and the GBM together may be able to tell us how GRBs actually work.”

Meegan points out that some bursts actually exploded when the Universe was less than a billion 

years old. “In fact, we may be seeing back to when the first stars formed,” he says. “GRBs may 

thus turn out to be our best window to the infancy of the Universe.”

3. Neutron Stars

By Robert Naeye

When the core of a massive star undergoes gravitational collapse at the end of its life, protons 

and electrons are literally scrunched together, leaving behind one of nature’s most wondrous 

creations: a neutron star. Neutron stars cram roughly 1.3 to 2.5 solar masses into a city-sized 

sphere perhaps 20 kilometers (12 miles) across. Matter is packed so tightly that a sugar-cubesized amount of material would weigh more than 1 billion tons, about the same as Mount 

Everest!

“With neutron stars, we’re seeing a combination of strong gravity, powerful magnetic and electric 

fields, and high velocities. They are laboratories for extreme physics and conditions that we 

cannot reproduce here on Earth,” says Large Area Telescope (LAT) science team member David 

Thompson of NASA’s Goddard Space Flight Center in Greenbelt, Md.

Most known neutron stars 

belong to a subclass known as 

pulsars. These relatively young 

objects rotate extremely rapidly, 

with some spinning faster than 

a kitchen blender. They beam 

radio waves in narrow cones, 

which periodically sweep 

across Earth like lighthouse 

beacons. But as GLAST 

Project Scientist Steve Ritz of 

NASA’s Goddard points out, 

“With magnetic fields trillions 

of times stronger than Earth’s, 

pulsar magnetic fields are highenergy particle accelerators.” 

The magnetospheres of some 

pulsars accelerate particles to 

such high energies that they 

are relatively bright gamma-ray 

sources. 

Astronomers have found less 

than 2,000 pulsars, yet there 

should be about a billion 

neutron stars in our Milky Way 

Galaxy. There are two reasons 

for this shortfall. One is age: 

most neutron stars are billions 

of years old, which means they 

have plenty of time to cool 

and spin down. Without much 

available energy to power 

emissions at various wavelengths, they have faded to near invisibility. But even many young 

pulsars are invisible to us with radio telescopes because of their narrow lighthouse beams. 

“Because pulsar beams are much broader in gamma rays, GLAST will allow us to detect some 

of the youngest, most energetic pulsars in our galaxy,” says GLAST Interdisciplinary Scientist 

Stephen Thorsett of the University of California, Santa Cruz. “Getting a much more complete 

sample of the Milky Way’s population of neutron stars is one of the most important ways that 

GLAST will advance our understanding of the life cycle of stars.”

FEATURES

FEATURES

Given their nasty environments, neutron stars would rank near 

the bottom of the list of interstellar vacation destinations. But 

they are a boon to GLAST scientists, who will study them as 

natural laboratories for some of our Universe’s most extreme 

physics. The gravity of these stellar corpses compresses 

matter to extraordinary densities, and warps the surrounding 

space-time. Ultrapowerful magnetic fields accelerate particles 

to speeds approaching that of light.

Credit: Casey Reed / Penn State University
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The EGRET instrument on NASA’s Compton Gamma-ray Observatory saw six pulsars, but the 

LAT has the sensitivity to find dozens or perhaps hundreds. Among these discoveries, scientists 

hope to find pulsars similar to Geminga, which is relatively bright in gamma rays but is strangely 

quiet in radio waves, perhaps because its radio beam doesn’t point toward Earth. Geminga is 

roughly 300,000 years old, which makes it middle-aged in the pulsar life cycle. If it weren’t so 

close to Earth (about 500 light-years), EGRET would not have seen it. The LAT will be able to 

see much fainter pulsars, many of which will be much older than Geminga. Pulsars spin-down 

as they age, and this should weaken particle acceleration, which in turn should cause their 

gamma-ray flux to weaken. The LAT should thus be able to tell scientists about this rate of 

decline, which in turn will yield precious clues about the particle-acceleration mechanism.

Finding new gamma-ray pulsars will be nice, but as LAT science team member Alice Harding 

of NASA’s Goddard notes, “GLAST is really about studying the physics of these sources.” For 

example, GLAST will probably be able to determine whether pulsar magnetic fields are so 

strong that gamma-ray photons packing more than about 4 or 5 GeV of energy can transform 

themselves into pairs of particles and antiparticles. EGRET observations suggest this process 

might be occurring in the magnetosphere of a pulsar in the constellation Vela. But EGRET 

did not have enough sensitivity at high gamma-ray energies to see if there is a sharp cutoff in 

gamma rays above 4 or 5 GeV. In the LAT’s first few months of operation, it should be able to 

see if the Vela pulsar exhibits this sharp cutoff — an unambiguous signature of pair production. 

“A neutron star is the only place where we can measure this effect,” says Harding.

EGRET observations showed that gamma rays dominate the total radiation emitted by young 

pulsars, which are rapidly spinning down. Moreover, EGRET data showed that variations 

in the high-energy gamma-ray emission probably arise from the changing view into the 

pulsar magnetosphere as the neutron star spins. The LAT will have the ability to map pulsar 

magnetospheres and provide unique information regarding the physics of the pulsed emission, 

and perhaps even answer the long-standing mystery of how the pulses are actually produced.

By monitoring the pulses of extremely fast rotators, known as millisecond pulsars, which rotate 

hundreds of times per second, GLAST will probably observe effects due to special relativity. 

“The pulses are so distorted by relativistic effects that we have to filter all of those out to figure 

out what’s really happening at the pulsar itself,” says Harding. She notes that these observations 

might dispel the common “lighthouse” model of pulsars, showing that what we see is really a 

relativistic distortion of the pattern emitted by the pulsar.

GLAST will also advance scientists’ understanding of how pulsars generate particle winds, and 

how these winds interact with the surrounding medium. The LAT may find several dozen new 

examples of pulsar wind nebulae, and provide much more detailed observations of the only 

example seen by EGRET: the one surrounding the pulsar in the Crab Nebula. Virtually nothing is 

known about the gamma-ray emission of pulsar wind nebulae in the region between 10 and 100 

GeV, and yet that might be where most of the exciting action is taking place. The LAT will fill in 

that gap.

GLAST’s other main instrument, the GLAST Burst Monitor (GBM), will likely pick up extremely 

energetic flares from neutron stars with ultra powerful magnetic fields. These so-called 

magnetars occasionally unleash flares that pack more energy in a fraction of a second than 

the Sun will emit in tens of thousands or even hundreds of thousands of years. The flares are 

probably ignited when a massive shift in the crust (a starquake) triggers a large-scale untwisting 

and rearrangement of magnetic-field lines, causing them to snap and release vast amounts of 

pent-up magnetic energy in the form of gamma rays, X rays, and particles.

But theorists lack a detailed understanding of this process. NASA’s Swift satellite has detected 

several of these events, including a superflare from the magnetar SGR 1806-20 on December 

27, 2004. 

The GBM and the LAT combined cover a much wider range of energies than Swift, so when 

combined with observations from other spacecraft, scientists may be able to assemble a more 

detailed picture of what powers these incredible outbursts.

4. Cosmic Rays and Supernova Remnants

By Robert Naeye

In the early 1900s, Austrian physicist Victor Hess discovered that particles from deep space 

incessantly bombard Earth’s atmosphere, producing showers of secondary particles that reach 

the surface. In one of the great misnomers of science, these particles came to be known as 

“cosmic rays.” But in reality, they have nothing to do with light rays. Instead, they are subatomic 

particles that have been accelerated to nearly the speed of light by energetic astrophysical 

processes whose sources have remained a mystery.

But after GLAST’s Large Area Telescope (LAT) 

collects data for a few years, there’s a very good 

chance that scientists will solve at least part of this 

mystery. For decades, scientists have pointed to 

a likely culprit for the acceleration of lower-energy 

cosmic rays: supernova remnants. These gaseous 

structures form when blast waves from exploding 

massive stars plow through interstellar material 

and sweep it up into shells. The shock waves 

that form in supernova remnants have the right 

amounts of energy to accelerate protons and other 

particles to the levels of energies measured in the 

lower-energy cosmic rays striking Earth’s upper 

atmosphere. Previous X-ray observations strongly 

suggest this is actually occurring. 

IMAGE AT”Cosmic rays, the highest-energy 

particles in nature, are thought to be formed when 

stars collapse and produce tremendous shock 

waves. GLAST will test this theory by measuring 

the spectra of gamma rays from the remnants of 

supernovae, where cosmic rays should be abundant,” says GLAST Interdisciplinary Scientist 

Charles Dermer of the Naval Research Laboratory in Washington, DC.

“The theory all seems right, but we’ve never been able to prove it. The LAT might just be the 

telescope that’s able to do it,” adds LAT science team member David Thompson of NASA’s 

Goddard.

According to theory, shock waves in supernova remnants can accelerate protons to energies 

1,000 times higher than can be achieved by the largest particle accelerators on Earth. The 

protons then collide with nearby interstellar material, producing a cascade of secondary particles 

known as pions (which are more massive than electrons, but less massive than protons and 

neutrons). Neutral pions (those lacking an electric charge) decay quickly into gamma rays of a 

characteristic energy around 67 MeV, ideal for detection with the LAT. 

When previous gamma-ray observatories looked toward the galactic plane, they saw an 

increase in gamma-ray flux right around 67 MeV, which proves that cosmic-ray particles are 

interacting with interstellar material throughout the Milky Way. “But we want to see that on a local 

scale,” says Thompson. “We want to see it happening at the sources, which are thought to be 

supernova remnants. The LAT has the sensitivity and spatial resolution to do the job.”

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This deep Chandra image shows 

Cassiopeia A (Cas A for short), the 

youngest known supernova remnant in the 

Milky Way. 

Credit: NASA/CXC/MIT/UMass Amherst/

M.D.Stage et al.
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The LAT’s energy range, however, is many orders of magnitude too low to enable scientists 

to decipher the origin ultra-high-energy cosmic rays, one of the great unsolved mysteries in 

astrophysics.

5. Milky Way Galaxy

By Robert Naeye

Not counting transient events such as gamma-ray bursts, the brightest object in the gammaray sky is the plane of our Milky Way Galaxy. This glow results from a vast sea of cosmic-ray 

particles slamming into interstellar gas and dust, generating gamma rays. In fact, 75% of the 

gamma rays in our galaxy come from these cosmic-ray interactions. This bright gamma-ray glow 

gives the GLAST science team a golden opportunity to study the structure, composition, and 

dynamics of the interstellar material that pervades our home galaxy.

But as Large Area Telescope science team member David Thompson of NASA’s Goddard, 

explains, “It’s not easy to understand something when you’re in the middle of it.” Adding to the 

complexity is the fact that our galaxy is filled with many different types of particles and energy 

sources, including protons, electrons, electromagnetic radiation, magnetic fields, and so forth — 

most of which have not been accurately measured. 

To study our galaxy, theorists create models of how these 

different particles interact with magnetic fields in different 

locations and with different strengths. Astronomers 

can then compare these models to actual observations 

made at radio, infrared, optical, ultraviolet, and X-ray 

wavelengths to see how well they match the data. The 

LAT will contribute vital data that will enable theorists to 

constrain and improve their models.

For example, the EGRET instrument on NASA’s 

Compton Gamma-ray Observatory saw hints that there 

may be clumps of gas in our galaxy that are not seen by 

radio telescopes. GLAST observations of the galactic 

plane should be able to help astronomers pin down 

whether or not these clumps are real. They might also 

reveal changes in the interstellar medium due to recent 

supernovae.

Having an accurate model of gamma-ray production within our galaxy is not only important 

in its own right, it is vital for the measurement of localized gamma-ray sources. The sources 

are seen against the bright background of the Milky Way glow. If the galaxy is not modeled 

correctly, then information about other objects could be distorted. As GLAST Program Scientist 

F. Rick Harnden Jr. notes, “The same gamma rays that measure galactic structure are also a 

background for other observations.”

6. The Gamma-ray Background

By Robert Naeye

From as far back as the late 1960s, orbiting observatories have found a diffuse background of 

gamma rays streaming from all directions. “If you had gamma-ray vision and looked at the sky, 

there would be no place that would be dark,” says Large Area Telescope (LAT) team member 

David Thompson of NASA’s Goddard.

To this day, astronomers have not pinned down the source of this gamma-ray background. The 

leading candidates are unresolved active galactic nuclei (AGN), especially blazars. NASA’s 

Chandra X-ray Observatory discovered, for example, that dust-enshrouded AGNs were 

responsible for a background glow seen in X rays. But astronomers don’t know enough about 

AGN and their gamma-ray-emitting properties to say with absolute certainty that AGNs are the 

source of the gamma-ray background. It’s quite likely that ordinary galaxies similar to our Milky 

Way are also an important component of the background, since they have the same cosmic-ray 

interactions with interstellar material that light up the plane of our galaxy.

The LAT has high enough sensitivity and spatial resolution that it should be able to confirm 

whether or not AGNs and ordinary galaxies are the culprit. LAT science team members will be 

able to correlate specific gamma-ray sources with objects seen at other wavelengths. They will 

also be able to measure the spectral properties of faint LAT sources to see if they match those 

of blazars.

”We should also be able 

to see starburst galaxies,” 

says GLAST Deputy Project 

Scientist Julie McEnery of 

NASA’s Goddard. These are 

galaxies that are forming 

stars in huge numbers. The 

most massive of these stars 

evolve quickly and explode as 

supernovae, producing swarms 

of cosmic rays in the process. 

“The gamma-ray flux from a 

galaxy should be a measure 

of the total energy flux from 

that galaxy. The LAT can try to 

verify that relationship between 

supernovae and the gammaray flux,” adds McEnery.

“If the background is not unresolved point sources, this would be a huge discovery, and would 

probably mean the glow is cosmological in origin,” says GLAST Project Scientist Steve Ritz of 

NASA’s Goddard. If AGNs and ordinary galaxies are not responsible, it could be the result of 

dark-matter particles annihilating one another or chain reactions caused by ultra-high-energy 

cosmic rays interacting with interstellar gas. Or it could come from a process that no one has yet 

conceived. But as Thompson says, “Occam’s razor dictates that we first test the obvious before 

going to the exotic.”

7. The Early Universe

By Robert Naeye

It may seem counterintuitive, but GLAST — a gamma-ray observatory — may provide crucial 

information about the amount of visible and ultraviolet light being emitted by the first stars to 

form in the Universe. It will be able to study this problem because, as LAT science team member 

David Thompson of NASA’s Goddard, explains, “Einstein’s equation E = mc2 works both ways.”

In other words, matter can be converted into energy (in the form of electromagnetic radiation), 

but energy can also be converted into matter. If a gamma-ray photon interacts with another 

photon, and if the two photons combined have a high enough energy, they can combine to 

become an electron and its antimatter counterpart, a positron. Visible-light and ultraviolet 

photons have enough energy to combine with gamma rays to make these interactions 

possible. The first generations of stars and galaxies must have bathed the early Universe in 

visible and ultraviolet photons, making such interactions probable enough that GLAST’s Large 

Area Telescope (LAT) should easily be able to detect this effect by seeing blazars fading and 

disappearing as it looks further and further back in time.

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Artist’s concept of the Milky Way 

Galaxy. GLAST will provide detailed 

information on where stars are 

forming. 

Credit: NASA JPL 

Starburst galaxies such as NGC 253, shown here, probably 

make up part of the gamma-ray background. 

Credit: Robert Gendler/Jim Mistin
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The effect depends greatly on a gamma ray’s energy, since the higher a photon’s energy, the 

more likely it is that it will meet another photon that it can interact with (or smash into) and 

produce matter particles. For example, below the energy of 1 GeV, a gamma ray can reach 

Earth from a redshift of 6 or higher, so LAT should be able to detect gamma-ray sources at 

those distances. (Redshift is a measure of how much an object’s light has been “stretched” by 

cosmic expansion, so the higher an object’s redshift, the further back we see it in time. A redshift 

of 6 corresponds to an era about 1 billion years after the Big Bang.) But gamma rays with 

energies of 100 GeV or higher should be absorbed en route to Earth if they originated from a 

source (such as a blazar) with a redshift of 6 or higher.

“GLAST will be able to measure how the amount of visible and ultraviolet light in the Universe 

changed over time by observing the gamma-ray flux as a function of distance and energy,” says 

GLAST Project Scientist Steve Ritz of NASA’s Goddard. “This effect kicks in at lower energies 

and greater distances.”

The EGRET instrument on NASA’s Compton Gamma-ray Observatory wasn’t sensitive enough 

to see enough very distant blazars and other gamma-ray sources to study this problem. In 

addition, it couldn’t detect gamma rays with high enough energies to provide meaningful results. 

“But the LAT has both capabilities, so it can do this experiment,” says Thompson. “It will give us 

a clue about the source of light in the very early Universe. This is an exciting prospect.”

“The more stars that formed in the early Universe, the more absorption of gamma rays,” 

adds Floyd Stecker of NASA’s Goddard. “These measurements will give us a handle on what 

happened in the distant past, which is why I call it photon archaeology.”

8. Solar System: Sun, Moon, and Earth

By Robert Naeye

Ordinary stars are simply not energetic enough to generate detectable levels of gamma rays. 

The one exception is the Sun, but only because of its close proximity to Earth. “If you exclude 

flares, the Sun is pretty quiet,” says LAT science team member David Thompson of NASA’s 

Goddard. 

But the Sun, of course, sporadically unleashes powerful flares, which spew particles into the 

solar system at high velocities. These flares can turn our star into an extremely bright gammaray source for several hours. Even though astronomers have studied solar flares for decades, 

they still don’t know how the Sun generates these outbursts. Astronomers also lack a detailed 

understanding of how the Sun accelerates particles that produce the gamma rays seen in flares.

GLAST could lead to important breakthroughs in this area. It will complement NASA’s Reuven 

Ramaty High Energy Solar Spectroscopic Imager (RHESSI) mission, a satellite launched in 

2002. RHESSI detects solar-flare gamma rays with energies up to about 20 MeV. The LAT will 

extend this range to higher than 300 GeV, which will enable astronomers to test theories that 

have been developed based on data from RHESSI and other instruments. 

The timing of the GLAST mission is ideal for solar studies, since the Sun recently passed 

through a minimum in its 11-year sunspot cycle. Solar activity is beginning to increase, and is 

expected to peak around 2011 or 2012. “No other instrument will be available to observe the 

Sun in the LAT’s energy band during the upcoming solar maximum,” says solar physicist Gerald 

Share of the University of Maryland, College Park.

Solar flares will also trigger the GLAST Burst Monitor (GBM), which covers an energy range 

that overlaps that of RHESSI. “The GBM may detect more than 100 flares containing nuclear 

radiation during this new cycle, Solar Cycle 24,” adds Share.

Scientists will use LAT and GBM data to test theories of flare production. According to most 

current theories, flares are produced when solar magnetic-field lines snap and then reconnect. 

These processes release staggering amounts of energy, and they could accelerate particles 

to energies high enough to produce gamma rays. Some solar flares produced such intense 

gamma-ray emission that they saturated the EGRET instrument on NASA’s Compton Gammaray Observatory. But with its more modern design, the LAT should provide crucial data that 

will help fill in the gaps in our understanding of solar flares and particle acceleration. Improved 

understanding of space weather, in turn, will make future human space missions safer. 

“Solar-flare particles can cause severe damage to satellites, and to astronauts if they are not 

protected,” says Thompson.

GLAST will even be able to detect 

gamma rays coming from the Sun 

during the quiet phases of its 11-year 

cycle. These gamma rays come from 

cosmic rays impacting the Sun. GLAST 

studies of the Sun’s quiescent phase 

should tell scientists quite a bit about 

the solar magnetic field

GLAST may also yield interesting 

results pertaining to other solar-system 

bodies. Surprisingly, the Moon is a 

moderately bright gamma-ray source. 

As Thompson says, “The only part of 

the electromagnetic spectrum where the 

Moon is brighter than the Sun is gamma 

rays.”

Being a cold, mostly inert object, the 

Moon is utterly incapable of producing 

gamma rays on its own. But cosmicray particles slamming into the lunar 

surface produce secondary gamma 

rays. The LAT will watch the Moon 

change position from hour to hour as it 

orbits Earth. The LAT will see higher-energy gamma rays emanating from the Moon than could 

be seen by EGRET, and the LAT’s spatial resolution is superior. However, scientists are not 

anticipating any dramatic discoveries.

Earth itself is also a bright gamma-ray source. Fortunately for us, our planet’s magnetic field and 

atmosphere prevent gamma rays from hitting the surface. But cosmic-ray interactions produce 

a steady and significant flux of gamma rays in the upper atmosphere. For the most part, the 

LAT will be looking away from Earth to avoid this emission. The BATSE instrument on Compton 

picked up low-energy gamma rays associated with lightning storms, along with energetic 

atmospheric phenomena at higher altitudes, such as jets and sprites. The GBM, and possibly 

even the LAT, will pick up many of these events.

Other solar-system objects are probably either too small or too far away to be detectable by 

GLAST.

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The Sun unleashed a flare on November 4, 2003 that 

could be one of the most powerful ever witnessed. 

GLAST will shed considerable light on the origin of 

these explosions and how particles are accelerated.

Credit: NASA SOHO
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9. Dark Matter

By Marcus Woo, Freelance Science Writer

The identity of dark matter — the mysterious stuff that makes up about 22% of the Universe’s 

energy contents — continues to elude scientists decades after they first inferred its existence. 

The leading candidate that might explain the fundamental make-up of dark matter is a 

hypothetical particle called the weakly interacting massive particle, or WIMP. But with GLAST, 

scientists may finally find clear evidence that dark matter is indeed made of WIMPs.

Gamma rays originate from a multitude of high-energy sources, such as black holes and 

exploding stars. But current theory suggests they can also come from WIMPs, which 

are massive particles that do not emit or absorb light. Such particles are predicted by 

supersymmetry, a theory that extends the highly successful Standard Model of particle physics.

According to supersymmetry, WIMPs 

act as their own antimatter particles. 

When two WIMPs interact, they 

annihilate each other and release 

a flurry of secondary particles as 

well as gamma rays. Using GLAST, 

scientists hope to find these highenergy signatures of dark matter 

in our galaxy. If they succeed, this 

discovery will help solve one of 

astronomy’s grandest mysteries.

“With GLAST, we hope to actually 

see individual dark-matter 

annihilations,” says theoretical 

physicist Michael Peskin of the 

Stanford Linear Accelerator Center 

(SLAC). Ted Baltz, a Kavli Institute 

for Particle Astrophysics and 

Cosmology (KIPAC) researcher 

who also works on GLAST, adds, 

“GLAST has the real possibility of 

making a fundamental contribution 

to understanding what galaxies are 

made of.”

Even though dark matter interacts much more weakly than ordinary matter, dark matter is not 

spread out evenly through space and should form clumps in and around galaxies. If dark matter 

is in fact composed of WIMPs, this clumping would improve the chances of these particles 

meeting and annihilating, producing steady streams of gamma rays detectable by GLAST’s 

Large Area Telescope.

The trick will be distinguishing gamma rays produced by dark-matter annihilations from those 

generated by numerous other sources in the Universe. To differentiate between the two, 

researchers have established a set of four guidelines:

•	 Supersymmetry predicts that WIMP annihilations will create gamma rays of particular 

wavelengths, distinct from those generated by other sources such as black holes or 

supernovae.

•	 Dark-matter annihilations should produce gamma rays exclusively, ruling out interactions that 

involve other forms of radiation.

•	 These signals should appear to GLAST not as point sources, but as large patches in the sky 

— some nearly twice as big as the full Moon.

•	 These streams of gamma rays should be continuous, a marked difference from the fleeting 

explosions of gamma-ray bursts, which last only a few milliseconds to several minutes.

If scientists find a signal with all of these characteristics, chances are good that they have found 

a source of WIMP annihilation.

GLAST will be running in parallel with numerous other dark-matter experiments, such as 

searches for WIMP collisions in underground detectors and attempts to manufacture WIMPs at 

the Large Hadron Collider (LHC) at the European Center for Nuclear Research (CERN) in

Switzerland starting in 2008. Given this activity, many scientists are confident the existence of 

WIMPS will be confirmed or refuted in the next few years.

"If GLAST detects these signals, it will be enormously important for both particle physics and 

astrophysics. It will represent a huge intellectual achievement and a big leap forward in our 

understanding of the Universe on the largest and smallest scales simultaneously," said Lynn 

Cominsky of Sonoma State University in Rohnert Park, California, leader of GLAST’s education 

and public outreach team.

10. Testing Fundamental Physics

By Robert Naeye

GLAST covers an energy range that will allow science team members to make sensitive tests 

of fundamental physics, perhaps finding violations to some of the field’s most cherished tenets. 

But as GLAST Deputy Project Scientist Julie McEnery of NASA’s Goddard cautions, "This is not 

guaranteed science; this is somewhat speculative."

For example, GLAST will be able to test whether light travels at the same speed in a vacuum 

regardless of wavelength. According to Albert Einstein’s special theory of relativity, all 

electromagnetic radiation should travel at the same speed, which has been measured to be 

299,792,458 meters (186,282.4 miles) per second. In other words, high-energy gamma-ray 

photons should zip across space at exactly the same speed as low-energy radio photons.

But some models of quantum gravity, which attempt 

to merge Einstein’s general theory of relativity with 

quantum mechanics, predict that extremely highenergy gamma rays could travel at a slightly different 

speed than other forms of light. According to quantum 

mechanics, space-time becomes turbulent at tiny 

scales, as quantum fluctuations cause virtual particleantiparticle pairs to continually form and annihilate. 

If quantum fluctuations also produce tiny black 

holes, as suggested by some versions of quantum 

gravity, very-high-energy gamma rays have such 

short wavelengths that they might actually "feel" this 

quantum turbulence, which could slightly boost or 

retard their velocity.

"GLAST may be able to test this prediction by running a very long race of 10 billion light-years," 

says GLAST Project Scientist Steve Ritz of NASA’s Goddard. If very-high-energy gamma rays 

from GRBs preferentially arrive at Earth slightly ahead of or behind low-energy gamma rays, 

this could indicate a violation in the principle that all light travels at the same speed in a vacuum. 

Even if GRBs tend to release high-energy gamma rays slightly before or after low-energy 

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According to supersymmetry, dark-matter particles known 

as neutralinos (which are often called WIMPs) annihilate 

each other, creating a cascade of particles and radiation 

that includes medium-energy gamma rays. If neutralinos 

exist, the LAT might see the gamma rays associated with 

their demise. 

Credit: Sky & Telescope / Gregg Dinderman. SPEED LIMIT?

SPEED OF LIGHT

186,282.4 miles

per second

Credit: NASA
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gamma rays, GLAST could notice that the lag time gets larger as GRB distances increase. "If 

this happens, and if we can exclude more mundane astrophysical explanations, this would be a 

huge discovery," says Ritz. "GLAST would truly carry us beyond Einstein."

GLAST could conceivably see the evaporation of tiny black holes — weighing around 1014

grams (100 million tons) — that formed moments after the Big Bang. At that time, the density 

variations in the Universe might have been high enough to allow small regions to collapse 

gravitationally into small black holes. Nobody knows whether such primordial black holes 

actually formed, but if they did, some might still be around in the Universe today. As first 

described by Stephen Hawking and others in 1974, black holes theoretically have finite lifetimes 

because they radiate away their mass in a quantum process. They literally evaporate into 

ordinary particles. The evaporation rate increases as the black-hole mass decreases, which 

explains why Hawking radiation is unobservable from stellar-mass black holes. At the end of 

their lives, tiny black holes undergo a runaway explosion into a shower of gamma rays and other 

particles. It’s possible that GLAST could detect gamma rays emitted by exploding black holes, 

and that would be a spectacular confirmation of the connection between quantum mechanics 

and general relativity.

The LAT might also pick up a strange phenomenon predicted by quantum theory, but which has 

only been observed in the laboratory: photon splitting. A very-high-energy gamma-ray photon 

could literally split into two lower-energy photons by tapping into a surrounding energy reserve, 

such as a neutron star’s magnetosphere. Compton Gamma-ray Observatory observations of 

the pulsar B1509-58 provided tantalizing hints for this process. GLAST observations of this and 

other pulsars could provide strong evidence that photon splitting is actually occurring in nature.

11. Unidentified Sources and the Unknown

By Robert Naeye

GLAST is certain to make contributions in a number of areas, such as the study of active 

galactic nuclei, gamma-ray bursts, and neutron stars. But for GLAST science team members, 

perhaps the most tantalizing possibility is the prospect of finding something entirely new and 

unexpected. "This is a relatively unexplored field, so the potential for major discoveries is very 

high," says LAT science team member David Thompson of NASA’s Goddard.

The history of astronomy shows that whenever instruments open a new window to the Universe, 

or make an order of magnitude improvement in capability, major discoveries almost always 

follow, often including the discovery of new classes of objects. GLAST represents such a giant 

leap over all previous gamma-ray satellites that it is not unrealistic to expect revolutionary 

findings (see article on pages 13-14).

A case in point can be seen when GLAST is compared to the EGRET instrument on NASA’s 

Compton Gamma-ray Observatory. EGRET logged 271 gamma-ray sources. But 172 of them 

— nearly two-thirds — remain unidentified, because EGRET could not pinpoint their location 

with sufficient precision to enable astronomers to associate them with known objects. "Since 

GLAST’s Large Area Telescope (LAT) can localize many objects to better than 1 arcminute, 

astronomers will be able to identify most of those sources," says GLAST Project Scientist Steve 

Ritz of NASA’s Goddard. 

Many of the unidentified point sources are probably in other galaxies — blazars. But a 

considerable number of the unidentified sources lie along the galactic plane, meaning that 

in all likelihood, they belong to our Milky Way Galaxy. Many of these sources are probably 

pulsars, whereas others could be supernova remnants, binary systems containing a black hole 

or neutron star, stars with powerful winds, or nebulae sculpted by pulsar winds. Some of the 

unidentified extragalactic sources may turn out to be clusters of galaxies, starburst galaxies, 

or ultraluminous infrared galaxies (known as ULIRGs). LAT observations should be able to pin 

down the nature of most of these objects. But as Thompson says, "There are surprises out there 

waiting to be found. Frankly, we’re hoping to be surprised when it turns out to be none of the 

above."

And because of the LAT’s major upgrade in sensitivity over EGRET, GLAST should see 

thousands of new point sources. "It might see 3,000 point sources, or it might see 9,000; we just 

don’t know. But we’re looking forward to the answer," says GLAST Project Scientist Steve Ritz of 

NASA’s Goddard.

GLAST Burst Monitor (GBM) Principal Investigator Charles “Chip” Meegan of NASA’s Marshall 

Space Flight Center in Huntsville, Alabama, echoes this assessment: “Although we can

anticipate some of the things that the GBM and the LAT will see, the most exciting results will be 

the surprises that always come from seeing what was previously invisible.”

“It will be interesting to see how wrong this all is after one or two years of taking data,” adds 

GLAST Deputy Project Scientist Julie McEnery of NASA’s Goddard. “I hope we are wrong on a 

lot of things, since it implies that the sky has surprises.”

LAT science team member Alice Harding of NASA’s Goddard concludes, “We’re going to find 

things that we don’t understand. Then we will have to figure out how to deal with it. It will be fun 

to study the sources we know about, but even more fun to solve the mysteries of the sources we 

can’t explain.”

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The EGRET instrument on NASA’s Compton Gamma-ray Observatory mapped 271 

sources. Nearly two thirds of these gamma-ray sources remain unidentified. 

Credit: EGRET Team 

AGN’s

Pulsars

Solar Flares

Galaxy (LMC)

Unidentified Sources
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GLAST LAUNCH AND OPERATION QUICK FACTS

HOW BIG IS THE SPACECRAFT? 

It is 9.2 feet (2.8 meters) high by 8.2 feet (2.5 meters) in diameter when stowed, where it is just 

under the 9-foot diameter allowed in the fairing. GLAST becomes a little bit taller and much 

wider after it is launched into space, when the Ku-band antenna deploys and the solar arrays 

are extended. 

Key Characteristics

Mass: The GLAST observatory weighs 9,487 lbs (4,303 kg)

Large Area Telescope (LAT) Mass: 6,149 lbs (2,789 kg)

Gamma-Ray Burst Monitor (GBM) Mass: 219 lbs (99.2 kg) 

Dimensions of the Spacecraft: 9.2 feet (2.8 meters) high x 8.2 feet (2.5 meters) in diameter 

when stowed

Power consumption: about 1,500 watts average over an orbit (solar panels 

supply up to 3,122 watts in sunlight)

Data downlink: 40 megabits per second, multiple contacts per day

Launch Site: Cape Canaveral Air Station, Fla.

Expendable Launch Vehicle: Delta II Heavy launch vehicle, with 9 solid rocket boosters. The 

solids are actually from the Delta III series (hence the term “heavy”), mounted on a 10 foot 

fairing and two stages

Launch Date: early 2008

Project Management: 

NASA’s Goddard Space Flight Center (GSFC)

Project Scientist: Steve Ritz, GSFC 

Project Manager: Kevin Grady, GSFC

LAT Management: 

Stanford Linear Accelerator Center (SLAC)

LAT PI: Peter Michelson, Stanford

GBM Management: 

NASA’s Marshall Space Flight Center (MSFC)

GBM PI: Charles (Chip) Meegan, MSFC 

GBM Co-PI: Jochen Greiner, Max Planck Institute for Extraterrestrial Physics

International Partners: 

LAT: France, Italy, Japan, and Sweden

GBM: Germany

GLAST Science Support Center: 

NASA’s Goddard Space Flight Center

Lead Education and Outreach: 

Lynn Cominsky, Sonoma State University

Spacecraft Contractor: 

General Dynamics Advanced Information Systems (AIS)

GLAST INSTRUMENTS

INTRODUCTION

The Gamma-ray Large Area Space Telescope (GLAST) is an international and multi-agency 

space observatory that will study the cosmos in the photon energy range of 8,000 electronvolts 

(8 keV) to greater than 300 billion electronvolts (300 GeV). An electronvolt is a unit of energy 

close to that of visible light, so GLAST will catch photons with energies thousands to hundreds 

of billions of times greater than those we see with our eyes (1 keV = 1,000 eV, 1 MeV = 

1,000,000 eV, 1 GeV = 1,000,000,000 eV).

GLAST carries two instruments: the Large Area Telescope (LAT) and the GLAST Burst Monitor 

(GBM). The LAT is GLAST’s primary instrument, and the GBM is the complementary instrument.

REQUIREMENTS FOR THE LAT AND GBM

Based on our knowledge of the gamma-ray sky from previous missions, scientists defined the 

following requirements for the GLAST instruments:

The Large Area Telescope (LAT)

1. Because the sky at gamma-ray energies has so many variable sources, the LAT must have 

a large field of view, over 2 steradians (one-fifth of the entire sky).

2. To identify and study sources accurately, the LAT must be able to measure the locations of 

bright sources to within 1 arcminute (about 1/30 of the diameter of the full Moon).

3. The study of gamma rays covers a broad energy range, so the LAT must catch photons 

with energies from 30 MeV to greater than 300 GeV. In particular, the LAT will have high 

sensitivity above 10 GeV, because almost nothing is known about cosmic objects at these 

energies.

4. Since gamma-ray bursts can release a torrent of gamma rays within a fraction of a second, 

the LAT must be able to measure gamma rays over short time intervals. 

5. Because scientists need long observations to understand many types of sources, the LAT 

should be able to operate for many years without degradation.

6. Because of the high flux of cosmic rays, which can mask the much smaller flux of 

gamma rays, the LAT must be able to reject 99.999% of signals generated by cosmic rays.

The GLAST Burst Monitor (GBM)

1. Gamma-ray bursts (GRBs) come from random directions of the sky, so the GBM must 

watch as much of the entire sky as possible at all times.

2. To gain the most information about GRBs, the GBM should be able to measure photon 

energies over a wide range, down to 8 keV and up to energies that overlap the LAT energy 

range.

3. Since GRBs last from mere microseconds to thousands of seconds, the GBM must be able 

to detect GRBs over a wide range of timescales.

INSTRUMENTS

QUICK FACTS

Image of the GLAST Satellite. 

Credit: NASA and Sonoma State

University, Aurore Simonnet
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THE INSTRUMENTS

Large Area Telescope (LAT)

The LAT has four subsystems that work together to 

detect gamma rays and to reject signals from the 

intense bombardment of cosmic rays. For every 

gamma ray that enters the LAT, it will have to filter out 

100,000 to one million cosmic rays, charged particles 

that resemble the particles produced by gamma rays. 

The four main subsystems are:

• Tracker

• Calorimeter 

• Anticoincidence Detector 

• Data Acquisition System 

With its very large field of view, the LAT sees about 

20% of the sky at any given moment. In sky-survey 

mode, which is the primary observing mode, the 

LAT will cover the entire sky every three hours. 

The observatory can also be pointed at targets of 

opportunity, and can slew autonomously when either 

instrument detects sufficiently bright gamma-ray bursts 

(GRBs). The LAT is at least 30 times more sensitive 

than any previous gamma-ray instrument flown in 

space, and will detect thousands of new sources during 

GLAST’s five-year primary mission.

The LAT was assembled at the Stanford Linear Accelerator Center (SLAC), but with substantial 

hardware contributions from partners in France, Italy, Japan, Sweden, and the U.S. SLAC also 

manages the collaboration. The Principal Investigator is Peter Michelson of Stanford University/

SLAC.

How the LAT Detects Gamma Rays and Rejects Cosmic Rays

1. A gamma ray enters the LAT. It first passes 

through the Anticoincidence Detector without 

producing a signal. 

2. The gamma ray interacts in one of 16 thin 

tungsten sheets. This interaction converts the 

gamma ray into an electron and a positron 

via pair production (governed by Einstein’s 

equation E=mc2).

3. The Tracker uses silicon strips to measure the 

paths of the electron and positron, allowing 

the LAT to determine the arrival direction of 

the gamma ray.

4. The electron and positron enter the 

Calorimeter, which measures the energies of 

the particles, and therefore the energy of the 

original gamma ray.

5. Unwanted cosmic-ray particles produce a signal in the Anticoincidence Detector, which 

tells the Data Acquisition System to reject the signal. The Anticoincidence Detector rejects 

99.97% of unwanted signals produced by cosmic rays that enter the LAT.

6. Software in the LAT Data Acquisition System also rejects, based on arrival direction, 

unwanted gamma rays that originate in Earth’s atmosphere.

Components of the LAT

Tracker 

The Tracker consists of a four-by-four 

array of tower modules. Each tower 

module consists of layers of silicon-strip 

particle tracking detectors interleaved 

with thin tungsten converter foils. The 

silicon-strip detectors precisely measure 

the paths of the electron and positron 

produced from the initial gamma ray. The 

pair-conversion signature is also used to 

help reject the much larger background 

of cosmic rays. 

Calorimeter

The Calorimeter measures the energy 

of a particle when it is totally absorbed. 

The LAT Calorimeter is made of a 

material called cesium iodide that 

produces flashes of light whose intensity 

is proportional to the energies of the 

incoming particle. The Calorimeter also 

helps to reject cosmic rays, since their pattern of energy deposition is different from that of 

gamma rays. 

Anticoincidence Detector (ACD)

The Anticoincidence Detector is the first line of defense against cosmic rays. It consists of 

specially formulated plastic tiles that produce flashes of light when hit by charged-particle cosmic 

rays (but not by gamma rays, which are electronically neutral). The ACD forms a “hat” that fits 

over the tracker.

Data Acquisition System (DAQ)

The Data Acquisition System is the brain behind the LAT. It collects information from the Tracker, 

the Calorimeter, and the Anticoincidence Detector and makes the initial distinction between 

unwanted signals from cosmic rays and real gamma-ray signals to decide which of the signals 

should be relayed to the ground. This system also does an on-board search for gamma-ray 

bursts. The DAQ consists of specialized electronics and microprocessors.

GLAST Burst Monitor (GBM)

The GBM consists of 12 detectors made of sodium iodide for catching X rays and low-energy 

gamma rays, and two detectors made of bismuth germanate for high-energy gamma rays. 

Together, they detect cover X rays and gamma rays in the energy range between 8 keV to 30 

MeV, overlapping with the LAT’s lower-energy limit. The GBM detectors will view the entire sky 

not occulted by Earth, and are expected to pick up about 200 GRBs per year, as well as solar 

flares and other transient events. The combination of the GBM and the LAT provides a powerful 

tool for studying GRBs over a very wide range of energies.

The development of the GBM and analysis of its observational data is a collaborative effort 

between the National Space Science and Technology Center in the U.S. and the Max Planck 

Institute for Extraterrestrial Physics (MPE) in Germany. The instrument is managed at NASA’s 

Marshall Space Flight Center in Huntsville, Alabama. Charles “Chip” Meegan of NASA’s Marshall 

is the Principal Investigator. In July 2007 Jochen Greiner of Max Planck replaced the now-retired 

INSTRUMENTS

Giselher Lichti as Co-P.I.

INSTRUMENTS

anticoincidence

detector

conversion foil

particle tracking

detectors

calorimeter

Credit: NASA

The LAT (silver box at the top) was 

integrated on the spacecraft at General 

Dynamics Advanced Information 

Systems in December 2006. 

Credit: NASA/General Dynamics 

Advanced Information Systems

Large Area Space Telescope

Sodium Iodide

Detectors (Nal)

Gamma-ray Large Area Space Telescope (GLAST)

Integrated on the Spacecraft at Spectrum Astro

Space Systems — December 2006

The LAT has 16 towers of particle detectors, seen 

here before the installation of the Anticoincidence 

Detector. Each tower contains a Tracker module and 

a Calorimeter module. The Data Acquisition System is 

located underneath the towers. 

Credit: SLAC
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How the GBM Detects Gamma-Ray Bursts

1 An X ray or low-energy gamma ray from deep 

space enters one of the 12 GBM low-energy 

detectors, which are flat disks made of a sodiumiodide material that produces a faint flash of light 

when struck. A photomultiplier tube detects the 

flash. 

2. The 12 detectors are located on opposite sides 

of the GLAST satellite, so they face different 

directions in the sky.

3. When gamma rays from a gamma-ray burst reach 

the GBM, the disk facing the burst will detect more 

gamma rays than the others.

4. By comparing the rate of signals from four or more 

detectors, the GBM can traingulate the arrival 

direction of the burst to within several degrees.

5. Two high-energy detectors made of bismuth 

germante pick up higher-energy gamma rays and 

measure their energies in much the same way as 

the low-energy detectors.

Components of the GBM 

Low-Energy Detectors

The low-energy sodium iodide detectors detect X rays with about 8 keV of energy up to gamma 

rays with about 1 MeV. They provide the locations of gamma-ray bursts to within several 

degrees, and they overlap in energy with other missions that detect GRBs, such as NASA’s 

Swift satellite. The low-energy detectors are mounted in four banks consisting of three detectors 

each. The 12 detectors are oriented in various directions so they face different parts of the sky. 

The GBM uses the signals from the low-energy detectors to 

detect burst locations.

High-Energy Detectors

The high-energy detectors are made of bismuth germanate, 

which is sometimes abbreviated BGO because germanate is a 

germanium oxide. They cover the energy range from about 150 

keV to about 30 MeV, providing a good overlap with the lowenergy detectors at the bottom end of the gamma-ray energy 

range, and with the LAT at the high end. Bismuth germanate 

is a high-density material that provides better sensitivity at 

high energies. The two high-energy detectors are positioned 

on opposite sides of the spacecraft, providing nearly full sky 

coverage.

Data Processing Unit

The electronics and microprocessors in the data processing 

unit receive and analyze the data from the low-energy detectors 

and high-energy detectors. It detects GRBs, determines their 

energies and arrival directions, and sends data to the GLAST 

spacecraft for transmission to the ground. 

GLAST WEB SITES

Here are links to GLAST web pages at various institutions.

USA

NASA’s GLAST mission

 http://www.nasa.gov/glast

NASA’s Goddard Space Flight Center

 http://glast.gsfc.nasa.gov/

Astrophysics Science Division at NASA’s Goddard Space Flight Center 

 http://astrophysics.gsfc.nasa.gov

Sonoma State University

 http://glast.sonoma.edu/

Space Sciences Laboratory at NASA’s Marshall Space Flight Center (GBM Site)

 http://gammaray.msfc.nasa.gov/gbm

Stanford Linear Accelerator Center (LAT Site)

 http://glast.slac.stanford.edu/

Stanford University (LAT Site) 

 http://glast.stanford.edu

University of California, Santa Cruz

 http://scipp.ucsc.edu/groups/glast/ 

University of Washington

 http://glast.phys.washington.edu/ 

U.S. Naval Research Laboratory

 http://heseweb.nrl.navy.mil/glast/index.html 

FRANCE

CEA Saclay

 http://www-dapnia.cea.fr/Sap/Activites/Projets/GLAST/index.html

École Polytechnique

 http://polywww.in2p3.fr/activites/physique/glast/

IN2P3 GLAST Web site

 http://GLAST.IN2P3.FR

Laboratoire de Physique Theorique & Astroparticules (LPTA Monpellier), France

 http://www.lpta.univ-montp2.fr/rubrique.php3?id_rubrique=87

GERMANY

Max Planck Institute for Extraterrestrial Physics

http://www.mpe.mpg.de/gamma/instruments/glast/GBM/www/index.html 

ITALY (sites in English)

INFN Bari University

http://www.ba.infn.it/~glast/ 

INFN Padova

 http://sirad.pd.infn.it/glast/index.html 

INFN Perugia

 http://glastweb.pg.infn.it/ 

INFN Pisa

 http://glast.pi.infn.it/ 

INFN Rome

 http://www.roma2.infn.it/research/comm2/glast/ 

Udine

http://www.fisica.uniud.it/~glast/udine.html

JAPAN

Hiroshima University

 http://www-heaf.hepl.hiroshima-u.ac.jp/glast/glast-e.html

SWEDEN

http://www.particle.kth.se/~tomiy/glast-sweden/glast.html

INSTRUMENTS

WEB SITES

GLAST Burst Monitor Principal 

Investigator Charles “Chip” 

Meegan, an astrophysicist 

at NASA’s Marshall Space 

Flight Center in Huntsville, 

Ala., tests the GLAST Burst 

Monitor. Credit: NASA/MSFC/

D. Higginbotham

Credit: NASA / David Thompson
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ELECTROMAGNETIC SPECTRUM BASICS

To be able to understand how GLAST works, you need to understand the electromagnetic 

spectrum. 

(“WHAT ARE GAMMA RAYS”)

What we call “light” is actually just a tiny fraction of the broad range of radiation on the 

electromagnetic radiation spectrum. The entire span stretches from very-low-energy radio 

waves through microwaves, infrared light, visible light, ultraviolet light, X rays, and finally to veryhigh-energy gamma rays. The processes producing photons (single particles of electromagnetic 

radiation) of each type of radiation differ, as do their energy, but all of the different forms of 

radiation are still just part of the electromagnetic spectrum. The only real difference between a 

gamma-ray photon and a visible-light photon is the energy. Gamma rays can have over a billion 

times the energy of the type of light visible to our eyes. 

In fact, gamma rays are so energetic that they are harmful to life on Earth. Luckily, Earth’s 

atmosphere absorbs gamma rays, preventing them from affecting life on the ground. But 

this poses a problem if you want to observe the Universe in gamma-ray light. The very 

atmosphere that protects us from gamma rays prevents us from directly observing them from 

the ground. Astronomical observations of gamma-ray sources in the GLAST energy range are 

therefore done with high-altitude balloons or satellites, above the protective blanket of Earth’s 

atmosphere. 

The high energy of gamma rays poses another problem: they can pass right through any lens or 

mirror, making it very difficult to focus them in a telescope. Astronomical observations, therefore, 

must rely on different technologies to view the gamma-ray universe. Scientists must make 

use of methods developed by particle physicists, who have long understood techniques for 

measuring high-energy particles. GLAST’s specialized astronomical instruments will therefore 

employ detectors used and perfected by physicists interested in the interactions of subatomic 

particles. 

EDUCATION AND PUBLIC OUTREACH PRODUCTS

Education and Public Outreach Products for GLAST from Sonoma State 

University

Online Activities can be found at: http://glast.sonoma.edu/teachers/online.html

Following are a list of activities and descriptions of them with the direct links to them:

• GLAST Large Area Tracker Simulator - See what happens when gamma rays and particles 

enter the GLAST Large Area Telescope at different angles and with different energies: 

 http://www2.slac.stanford.edu/vvc/glastlat/lat_simulator.html

• Space Mysteries - Can you solve the mysteries? Two space mysteries featuring GLAST 

science: Found at: http://mystery.sonoma.edu/

The GLAST Educator Ambassadors program: http://glast.sonoma.edu/ambassadors/index.

html GLAST supports 10 Educator Ambassadors that help develop, test, and disseminate 

educational materials based on science from NASA’s Astrophysics Division of the Science 

Mission Directorate. There are now 16 Educator Ambassadors in this program. 

• Meet the Educator Ambassadors - the people, their biographies, and their missions: 

http://glast.sonoma.edu/ambassadors/ambassadors.html

• Educator Ambassadors in the News - recent news articles featuring the Educator 

Ambassadors: http://epo.sonoma.edu/ambassadors/ambassador_news.html

• Upcoming Events - a list of workshops being conducted by the Educator Ambassadors: 

http://epo.sonoma.edu/ambassadors/events.php

The Global Telescope Network - Use real astronomical data in your classroom: 

http://gtn.sonoma.edu/public/

GLAST Classroom Materials: http://glast.sonoma.edu/teachers/teachers.html

Printed Materials:

• Black Hole Resource Area: http://glast.sonoma.edu/teachers/blackholes/index.html

• Supernova Educator Guide - The GLAST and XMM-Newton E/PO programs have developed 

a set of formal activities and background materials about supernovae. This is being jointly 

developed for GLAST and XMM-Newton. Found at: http://xmm.sonoma.edu/edu/supernova/

index.html

• TOPS Learning Systems has developed a three-booklet series of activities based on the 

math and science of the GLAST mission. In the TOPS tradition, each booklet has activities 

which use simple, inexpensive household materials (such as coins, paper plates, thread 

spools, etc.) in clever ways. http://topscience.org/

• Download “Far Out Math!” PDF (11.5Mb): http://glast.sonoma.edu/teachers/topsmod1.pdf

• Presentation: TOPS Far Out Math! http://glast.sonoma.edu/teachers/topsmod1.pdf

• Booklet 2, "Scale the Universe": The size and scale of the Universe are among the most 

difficult concepts to understand. This booklet gently takes students through the orders-ofmagnitude of the Universe starting with the familiar human scale, then going down to the 

infinitesimal and out to the astronomical. 

• Download “Scale the Universe” PDF (3.7Mb): http://glast.sonoma.edu/teachers/scale_

universe.pdf

• Booklet 3, "Pi in the Sky": These activities teach about radians and degree, angles, parallax, 

and apparent sizes of objects. Students will measure the apparent sizes of objects at various 

distances and learn about how we can measure the sizes of distant objects.

Download "Pi in the Sky" PDF (20Mb) : http://glast.sonoma.edu/teachers/pi_in_the_sky.pdf

Presentation: TOPS Scale the Universe and Pi in the Sky 

SCIENCE

E/PO

Wavelength (meters)

Radio Microwave Infrared Visible Ultraviolet X-ray Gamma Ray

Buildings Humans Honey Bee Pinhead Protozoans Molecules Atoms Atomic Nuclei

About the size of...

103 10-2 10-5 .5x10-6 10-8 10-10 10-12

Credit: NASA / Ruth Jennings
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Active Galaxy Education Unit 

The GLAST E/PO team has developed a set of three activities to teach students about active 

galaxies. All three activities are aligned with the national science and mathematics standards. A 

beautiful poster illustrating an Active Galaxy features one of the three activities on the reverse 

side.

• Active Galaxies Poster: http://glast.sonoma.edu/images/agn.html

• Active Galaxies Poster without the text: http://glast.sonoma.edu/images/agnnotext.html

• Educator Guide: Download PDF (3.36 Mb): http://glast.sonoma.edu/teachers/agn/

agnacti027.pdf

• Educator Guide (HTML Version): http://glast.sonoma.edu/teachers/agn/index.html

• Active Galaxy Pop-up Book - This short, innovative book for ages 8-12 has three separate 

activities, including a popup 3D galaxy showing its features, the “Tasty Active Galaxy” activity 

where kids can make their own edible black hole, and a whimsical story about supermassive 

black holes called “How the Galaxy Got Its Jets”. Although designed for younger children, it 

can be enjoyed by people of all ages (especially eating the black hole):

http://glast.sonoma.edu/teachers/popup.html

Miscellaneous GLAST Education Products

• GLAST Mission Poster - features an artist’s drawing of the GLAST satellite in orbit: http://

glast.sonoma.edu/images/glaunchflp03.html

• The GLAST Cube - images and text from the GLAST “magic cube”: http://glast.sonoma.edu/

resources/cubeimages/cube.html

• GLAST Public Brochure: http://glast.sonoma.edu/resources/brochure/glastbroch04.pdf

• GLAST Race Trading Card Game — Who will be the first to build, launch and make 

observations with GLAST? http://glast.sonoma.edu/teachers/race.html

• GLAST Sticker - Features artist’s interpretation of an active galaxy as well as an image of the 

satellite: http://glast.sonoma.edu/resources/sticker/glast_sticker.html

Additional GLAST Education and Public Outreach Efforts at UC Santa Cruz:

• The BALLOON Program: http://scipp.ucsc.edu/outreach/ballon.html

• SCIPP Tesla Coil Show: http://scipp.ucsc.edu/outreach/tesla/teslacoil/index.html

• GLAST on MYSPACE.COM: http://www.myspace.com/GLAST

GLAST SCIENCE GLOSSARY

Source: http://glast.sonoma.edu/science/gru/glossary.html

Accretion — The process whereby a compact object such as a black hole or neutron star

captures matter from a normal star or diffuse cloud. 

Active galactic nuclei (AGN) — The central region of some galaxies that appears as an 

extremely luminous point-like source of radiation. They are powered by supermassive black 

holes accreting nearby matter. 

Annihilation — The process whereby a particle and its antimatter counterpart interact, 

converting their mass into energy according to Einstein’s famous formula E = mc2. For example, 

the annihilation of an electron and positron results in the emission of two gamma-ray photons, 

each with an energy of 511 keV. 

Anticoincidence Detector — A system on a gamma-ray observatory that triggers when it 

detects an incoming charged particle (cosmic ray) so that the telescope will not mistake it for a 

gamma ray. 

Antimatter — A form of matter identical to atomic matter, but with the opposite electric charge.

Arcminute — One-sixtieth of a degree on the sky. Like latitude and longitude on Earth’s 

surface, we measure positions on the sky in angles. A semicircle that extends up across the sky 

from the eastern horizon to the western horizon is 180 degrees. One degree, therefore, is not a 

very big angle. An arcminute is an even smaller angle, 1/60 as large as a degree. The Moon and 

Sun are each about half a degree across, or about 30 arcminutes. If you take a sharp pencil and 

hold it at arm’s length, then the point of that pencil as seen from your eye is about 3 arcminutes 

across.

Astronomy — The scientific study of the Universe and objects beyond Earth, especially the 

positions, dimensions, distribution, motion, composition, energy, and evolution of celestial bodies 

and phenomena. 

Astrophysics — A combination of physics and astronomy that deals principally with the physical 

processes of celestial bodies and phenomena. 

Atmospheric Cherenkov Telescopes (ACTs) — Ground-based telescopes that indirectly 

detect very-high-energy gamma rays from space. These gamma rays interact with atoms in 

Earth’s atmosphere, producing Cherenkov Light.

Atom — The smallest unit of an element which keeps the element’s characteristics. An atom 

consists of one or more protons and neutrons (except for hydrogen, which may have no 

neutrons) in a nucleus, with one or more electrons outside the nucleus. 

BATSE — The Burst and Transient Source Experiment on board the Compton Gamma-ray 

Observatory. BATSE made all-sky observations of gamma-ray bursts and flares, as well as 

observing many other objects between 10 keV and 5 MeV. 

Big Bang — A theory of cosmology in which the Universe once existed in a hot, dense state, 

and has been expanding ever since. 

Binary stars — Two stars that orbit around a common center of mass. 

Black hole — An object with gravity so strong that nothing, not even light, can escape. 

Blazar — A type of active galactic nucleus (AGN) that often appears as a point-like source of 

bright, highly variable radiation. Astronomers think blazars are AGN that have a jet of matter and 

radiation pointed directly at Earth.

Calorimeter — A detector that absorbs particles and photons, producing an electrical signal 

proportional to the total incident energy. It can be used to measure a gamma ray’s energy.

Cherenkov light — Blue light emitted when particles travel through a medium faster than light 

travels through that medium.

Compton Gamma-ray Observatory (CGRO) — A NASA gamma-ray mission that was 

launched in April 1991, and which re-entered Earth’s atmosphere in June 2000. CGRO had 

four experiments: BATSE, OSSE, COMPTEL, and EGRET, which together spanned the energy 

range 10 keV to 30 GeV. 

COMPTEL — The Imaging Compton Telescope experiment on board the Compton Gamma-ray 

E/PO

Observatory. COMPTEL detected gamma rays in the energy range 100 keV to 30 MeV. 

GLOSSARY
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Converter — Material in which the pair-production process takes place. Due to conservation of 

momentum and energy, pair production cannot take place in empty space.

Cosmic rays – Elementary particles or atomic nuclei that travel through interstellar space at 

speeds approaching that of light. 

Cosmology — The study of the origin, structure, and evolution of the Universe. 

Dark matter — A non-luminous gravitational component of the Universe invoked to explain the 

internal motions of galaxies and the motions of galaxies within clusters of galaxies. 

Degree — A unit of angular size. One degree is 1/360 of a full circle, or, conversely, there are 

360 degrees in a circle. 

Density — The ratio between the mass of an object and its volume. 

Diffuse galactic emission — Non-point-source gamma-ray emission from the plane of our 

Milky Way Galaxy. Mostly due to interactions of cosmic rays with interstellar material. 

EGRET — Energetic Gamma Ray Experiment Telescope on board the Compton Gamma-ray 

Observatory. It operated from 30 MeV to 30 GeV. 

Electromagnetic spectrum — All the different wavelengths of light, which is also called 

electromagnetic radiation. Only a small portion of this spectrum is visible to the human eye. 

From lowest to highest energy, the broad energy bands within this spectrum are: radio, 

microwave, infrared, visible, ultraviolet, X rays, and gamma rays. 

Electron — An elementary particle with a single negative charge, and a mass of about 511 keV. 

Electronvolt (eV) — A unit of energy, sufficient to excite atoms to emit visible light. 

(1 keV=1,000 eV, 1 MeV=1,000 keV, 1 GeV=1,000 MeV).

Extragalactic — Outside of, or beyond, our own Milky Way Galaxy. 

Flux — A measurement of the brightness of a source. 

Frequency — A property of a wave that describes how many wave patterns or cycles pass by in 

a period of time. Frequency is often measured in Hertz (Hz), where a wave with a frequency of 1 

Hz will pass by at 1 cycle per second. 

Galaxy — A component of our Universe made up of gas, a large number (usually more than a 

million) of stars, and dark matter. A galaxy is held together by gravity. 

Gamma ray — A photon more energetic than an X ray (more than about 50 keV). Gamma rays 

are created from nuclear reactions or particle accelerations. Gamma rays are the most energetic 

photons of the electromagnetic spectrum.

Gamma-ray background — A diffuse glow of gamma rays seen in all directions. Most of the 

background is probably due to unresolved blazars and other AGN.

Gamma-ray burst (GRB) — A brief but intense torrent of gamma-ray emission from a point 

source in deep space. Astronomers think most GRBs are produced by exploding stars.

General theory of relativity — Einstein’s theory of gravity that unites special relativity, 

Newton’s laws of gravitation, and the insight that gravitational acceleration can be described by 

the curvature of space and time.

GLAST — Gamma-ray Large Area Space Telescope. 

GLAST Burst Monitor (GBM) — The instrument on GLAST that is specifically designed to 

detect gamma-ray bursts.

Gravity — The attractive force of an object with mass on another object. The gravitational force 

between two objects depends on their masses and the distance between them. 

Hawking radiation — A theoretical faint glow of particles and radiation from a black hole, 

predicted by Stephen Hawking as a result of quantum-mechanical effects.

Infrared — The region of the electromagnetic spectrum with wavelengths in the range of 

2.5 x 10-6 meters to 7 x 10-7 meters. Infrared photons are between visible-light photons and 

microwaves in the electromagnetic spectrum. 

Interstellar — Material or space between the stars.

Ion — An atom or molecule that has lost or gained one or more electrons and has become 

electrically charged as a result. 

Ionization — The process by which ions are produced, typically occurring by collisions with 

atoms or electrons, or by interaction with electromagnetic radiation.

Jet — A collimated stream of relativistic particles and photons which flows from a central source 

(often a black hole).

Kelvin (K) — A temperature scale (named after Lord Kelvin) that measures an object’s 

temperature above absolute zero, the theoretical coldest possible temperature. The temperature 

in Kelvins can be converted to Celsius by the equation K = 273 + C and to Fahrenheit by K = 

273 + 5/9 * (F - 32).

Kilogram (kg) — A unit of mass. One kilogram is defined as the mass of one liter (1,000 cubic 

centimeters) of water at 277 Kelvin. 1 kg = 2.2046 pounds.

Large Area Telescope (LAT) — The primary science instrument on GLAST.

Light — Generally used to mean electromagnetic radiation that is visible to the human eye. 

Sometimes used to mean all wavelengths of electromagnetic radiation. 

Light-year — The distance light travels in 1 year: 9.5 trillion kilometers or 5.9 trillion miles.

Luminosity — The rate at which a star or other object emits energy, usually in the form of 

electromagnetic radiation. 

Magnetar — A neutron star with an extraordinarily powerful magnetic field.

Magnetic field — The region of space around a magnetic body or a current-carrying body 

where objects can be affected by the magnetic forces due to the body or current. 

Magnetosphere — The immediate region around a body with a magnetic field where particle 

behavior is controlled by that field. 

Mass — A measure of the total amount of material contained in a body. 

Meter (m) — The fundamental international unit of length, defined as the length of the 

path traveled by light in vacuum during a period of 1/299,792,458 second. One meter is 

approximately 39.4 inches. 

Microwave — The region of the electromagnetic spectrum with wavelengths in the range of 

2.5 x 10-6 meters to 10-4 meters. Microwave photons are between infrared and radio in the 

electromagnetic spectrum. 

Milky Way — The name of our own Galaxy, which contains a flattened disk of stars about 

100,000 light-years across, along with star clusters, interstellar gas and dust, and vast amounts 

of dark matter.

NASA — The National Aeronautics and Space Administration, founded in 1958. www.nasa.gov

Nebula — A diffuse cloud of interstellar gas and dust. 

Neutron — A particle commonly found in the nucleus of an atom with approximately the mass of 

a proton, but with zero electrical charge. 

Neutron star — An extremely dense core of a dead star that exploded as a supernovae. 

Neutron stars have diameters of about 20 kilometers and masses of about 1.5 times that of our 

Sun. A neutron star internally supports itself against gravity by pressure from the strong nuclear 

force between neutrons.

Nucleus (plural: nuclei) — The positively charged central portion of an atom that comprises 

nearly all of the atomic mass and that consists of protons and (except for the simplest form 

of hydrogen) neutrons. In general, the central point, group, or mass about which gathering, 

concentration, or accretion takes place. 

Occam’s Razor — A scientific principle that states that the simplest explanation for a 

phenomenon is usually the most desirable explanation.

Orbit — The path of an object that is moving around a second object or point under the 

influence of gravity. 

OSSE — Oriented Scintillation Spectrometer Experiment on board the Compton Gamma-ray 

Observatory (operated between 50 keV and 10 MeV).

Pair production — A physical process in which a gamma-ray photon transforms itself into a 

particle and its antimatter counterpart.

Parallax — The apparent motion of a relatively close object compared to a more distant 

background as the location of the observer changes. Astronomically, it is half the angle which a 

star appears to move as Earth moves from one side of the Sun to the other. 

Particle accelerator — Any machine or natural object that can accelerate charged particles, 

such as electrons, positrons, or protons to speeds approaching that of light. 

Photomultiplier tube — A device that produces electrical signals from faint pulses of light, 

using the photoelectric effect to produce a few electrons from incident light, then multiplying the 

GLOSSARY

number of electrons by a cascade process.

GLOSSARY
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Photon — The fundamental “particle” of light. The energy of a photon is proportional to its 

frequency. 

Photon splitting — A physical process in which a very-high-energy gamma-ray photon can 

borrow energy from an external source, such as a very strong magnetic field, and split into two 

lower-energy photons.

Pion — An unstable nuclear particle with a rest mass between that of an electron and a proton. 

Also known as the pi meson. 

Positron — The antimatter counterpart of the electron, essentially an electron with a positive 

charge.

Primordial black hole — A black hole that formed in the very early Universe from a dense 

concentration of matter. Primordial black holes have never been observed.

Proton — A positively charged particle commonly found in the nucleus of an atom. 

Pulsar — A type of neutron star with a beam of emission that sweeps around as the star rotates. 

Pulsar wind nebula — A cloud created from gas and particles blown off a neutron star.

Quantum fluctuations — A short-lived change in the state of empty space due to quantum 

mechanics. Quantum fluctuations can often involve the rapid production and annihilation of 

virtual pairs of particles and their antimatter counterparts.

Quantum gravity — Theories that attempt to merge Einstein’s general theory of relativity and 

quantum mechanics.

Quantum mechanics — The branch of physics dealing with the interactions of matter, energy, 

and space at tiny scales.

Quasar — A type of active galactic nucleus with a core that is extremely luminous in visible light 

and sometimes other wavelengths as well.

Radiation — The process in which energy is emitted as electromagnetic waves, or the energy 

itself. 

Radio — The region of the electromagnetic spectrum with wavelengths longer than 10-4 meters. 

Radio photons have the lowest energies and longest wavelengths in the electromagnetic 

spectrum. 

Radio galaxy — A galaxy with strong radio emission, usually powered by an active galactic 

nucleus.

Redshift — The shift of spectral lines to longer wavelengths either due to the motion of the 

source away from the observer, the expansion of the Universe, or very strong gravity. 

Resolution — The size of the smallest detail visible in an image. Low resolution shows only 

large features, high resolution shows many small details. 

Satellite — A natural or artificial body that revolves around a more massive body. For example, 

the Moon is a satellite of Earth. 

Scintillation — The emission of light that occurs when electrons or positrons excite a substance 

in a transparent material they are passing through. 

Seyfert galaxy — A type of active galactic nucleus that is very luminous, but not as luminous as 

a quasar or blazar.

Shock waves — A compressional wave triggered by an explosion or energetic event.

Silicon-strip detectors (SSD) — Detectors made of tiny strips of silicon, which create voltage 

pulses when traversed by high-energy charged particles, such as protons, electrons, or 

positrons. 

Solar flare — A burst-like emission of radiation and particles from a magnetic disturbance on 

the Sun.

Solar mass — A unit of mass equivalent to the mass of the Sun: 1 solar mass = 2 x 1030

kilograms. 

Special theory of relativity — Einstein’s theory of motion that relates mass and energy, and 

that states that no information can travel faster than the speed of light in a vacuum.

Spectrum (plural: spectra) — A plot of the intensity of light as a function of frequencies; the 

distribution of wavelengths and frequencies. 

Speed of light (in a vacuum, c) — The speed at which electromagnetic radiation propagates 

in a vacuum; it is defined as 299,792,458 meters per second (186,282.4 miles per second). 

Einstein’s special theory of relativity implies that no information can travel faster than the speed 

of light. 

Standard Model of particle physics — A highly successful theory that describes three of the 

four known fundamental forces of nature and the elementary particles that make up all matter.

Star — A large ball of gas that creates and emits its own radiation through the process of 

nuclear fusion, or the core of star that once created and emitted its own radiation through fusion.

Starburst galaxy — A galaxy undergoing an intense round of star formation.

Strong nuclear force — A short-range but powerful nuclear force that operates within an atomic 

nucleus to hold protons together despite their positive electric charges.

Subatomic particles — Particles that are smaller than an atom. Examples include the electron, 

proton, and neutron. 

Superluminal motion — An optical illusion in which material appears to be traveling faster than 

the speed of light.

Supernova — An extremely energetic and life-ending explosion of a star.

Supernova remnant — The outwardly expanding outer portions of a star that exploded as a 

supernova and the expanding gaseous shell swept up by a supernova shock wave. 

Supersymmetry — An extension of the Standard Model of particle physics, supersymmetry 

hypothesizes the existence of a complete set of additional particles which complement those 

that are known to exist. Thus far, no supersymmetric particles have been detected. In some 

theories, the least massive supersymmetric particle (often called a WIMP) could be a good 

candidate for dark matter. 

Swift — A NASA satellite launched in 2004 that was specifically designed to study gamma-ray 

bursts.

Tracker — The part of a high-energy gamma-ray detector that is used to determine the 

trajectory of the incoming gamma-ray. For a silicon-strip detector-based tracker, the trajectories 

of electron-positron pairs are recorded. These pairs are produced by the converter. 

Transient — A source that appears and then disappears, such as a gamma-ray burst. 

Ultraviolet — The region of the electromagnetic spectrum with wavelengths in the range of 

10-9 meters to 4 x 10-7 meters. Ultraviolet photons are between X rays and visible light in the 

electromagnetic spectrum. 

Vacuum — A space largely devoid of matter. 

Visible light — The region of the electromagnetic spectrum seen by the human eye, with 

wavelengths in the range of 4 x 10-7 meters to 7 x 10-7 meters. Visible-light photons are between 

ultraviolet and infrared. 

Wavelength — The distance between the crest (or trough) on a wave and the crest (or trough) 

in the next cycle.

White dwarf — The exposed core of a relatively low-mass star after it has ejected its 

atmosphere; it’s approximately the size of Earth but with the mass of our Sun.

WIMP — Weakly Interacting Massive Particle; elementary particles predicted by supersymmetry 

but which have not been observed. WIMPS might comprise some or most of the Universe’s dark 

matter.

X ray — The region of the electromagnetic spectrum with wavelengths in the range of 

10-12 meters to 10-9 meters. X rays are between gamma rays and ultraviolet light in the 

electromagnetic spectrum. 

X-ray binary — A binary star where one of the stars is a collapsed object such as a white dwarf, 

neutron star, or black hole. The separation between the stars is small enough so that matter is 

transferred from the normal star to the collapsed star, producing X rays in the process. 

GLOSSARY

GLOSSARY
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GLAST-RELATED ACRONYMS

ACD. The LAT Anticoincidence Detector Subsystem

ACT. Atmospheric Cherenkov Telescope

AGILE. Astro-rivelatore Gamma a Immagini Leggero (Light Astro Gamma 

Imaging Detector)

AGN. Active Galactic Nuclei

AIS. Advanced Information Systems (General Dynamics)

ASI. Italian Space Agency

BATSE. Burst and Transient Source Experiment on CGRO

BGO. Bismuth Germanate

Bps. Bits per second

C.R.. Cosmic Ray

CAL. The LAT Calorimeter Subsystem

CANGAROO. Collaboration between Australia and Nippon for a Gamma-Ray

Observatory in the Outback

CCD. Charge-coupled Device

CEA. Commissariat a l’Energes Atomique

CENBG. Centre d’etudes Nucleaires de Bordeaux Gradignan

CERN. Centre European pour la Recherche Nucleaire or the European Center 

for Nuclear Research

CGRO. Compton Gamma-ray Observatory

CNRS. Centre National de la Recherche Scientifique

COMPTEL. Compton Telescope on CGRO

COSB. European Gamma-ray Astronomy Satellite

DAPNIA. Departement d’Astrophysique, de physique des Particules, de physique 

Nucleaire et de L’Instrumentation Associee

DAQ. Data Acquisition System 

DESY. Deutsches Electron-Synchrotron

DOE. Department of Energy

EDAQ. the LAT Electronics, Data Acquisition and Flight Software Subsystem

EGRET. Energetic Gamma Ray Experiment Telescope on CGRO

EPO. Education and Public Outreach

FOV. Field of View

GBM. GLAST Burst Monitor

Gbps. Gigabits per second

GCN. Gamma-ray Burst Coordinate Network

GeV. Giga (billion) electronvolts

GIOC. GBM Instrument Operations Center

GITD. GLAST Instrument Technology Development

GLAST. Gamma-ray Large Area Space Telescope

GRB. Gamma-ray Burst

GRO. Gamma-ray Observatory

GSFC. NASA’s Goddard Space Flight Center

GSI. Gesellschaft für Schwerionenforschung or the Society for Heavy Ion 

Research

HE. High Energy

HEAO. High Energy Astrophysics Observatory

HEASARC. High Energy Astrophysics Science Archive Research Center

HEPL. W.W. Hansen Experimental Physics Laboratory at Stanford University

H.E.S.S.. High Energy Stereoscopic System

HETE2. High Energy Transient Explorer

IAU. International Astronomical Union

IDS. Interdisciplinary Scientist

IN2P3. Institut National de Physique Nucleaire et de Physique des Particules

INFN. Istituto Nazionale Di Fisica Nucleare (Italy)

INTEGRAL. International Gamma-Ray Astrophysics Laboratory (European Space 

Agency)

IOC. Instrument Operations Center

ISAS. Institute for Space and Astronautical Science, Japan

JGC. Japanese GLAST Collaboration

Kbps. Kilobits per second

KEK. National Laboratory for High Energy Physics, Japan

KeV. Kilo (thousand) electronvolts

kg. Kilogram

KSC. NASA’s Kennedy Space Center

KTH. Royal Institute of Technology, Sweden

LAT. GLAST Large Area Telescope

LEO. Low Earth Orbit

LHC. Large Hadron Collider

LIOC. LAT Instrument Operations Center

LOF. LAT Operations Facility

MAGIC. Major Atmospheric Gamma Imaging Cherenkov

Mbps. Megabits per second

MeV. Mega (million) electronvolts

MILAGRO. Multiple Institution Los Alamos Gamma Ray Observatory

MOC. Mission Operation Center

MPE. Max Planck Institute for Extraterrestrial Physics

MSFC. NASA’s Marshall Space Flight Center

NaI. Sodium Iodide

NAS. National Academy of Sciences

NASA. National Aeronautics and Space Administration

NCST. Naval Center for Space Technology

NRL. Naval Research Laboratory

NSF. National Science Foundation

NSSTC. National Space Science and Technology Center

OSS. NASA’s Office of Space Science

OSSE. Oriented Scintillation Spectrometer Experiment on CGRO

PCC. Laboratoire de Physique Corpusculaire et Cosmologie

PI. Principal Investigator

RXTE. Rossi X-Ray Timing Explorer

SCIPP. Santa Cruz Institute of Particle Physics at UCSC

SGC. Swedish GLAST Collaboration

SLAC. Stanford Linear Accelerator Center

SNR. Supernova Remnant

SSU. Sonoma State University

SU. Stanford University

SU-HEPL. Stanford University Hanson Experimental Physics Laboratory

TeV. Trillion electronvolts

TKR. The LAT Tracker Subsystem

UAH. University of Alabama at Huntsville

UCSC. University of California, Santa Cruz

ULIRG. Ultraluminous Infrared Galaxy

VERITAS. Very Energetic Radiation Imaging Telescope Array System

WIMP. Weakly Interacting Massive Particle

ACRONYMS

ACRONYMS
National Aeronautics Space Administration

www.nasa.gov

Credit: All three images - S.W. Digel (NASA/GSFC)