# Presentation: 085800

## Surveying the TeV Sky with Milagro and HAWC

**Surveying the TeV Sky with Milagro and HAWC**

**Brenda Dingus **
**Los Alamos National Lab**
- dingus@lanl.gov

_**Outline:**_
**High Energy Particle Astrophysics**
**Gamma Ray Observatories**
**Milagro Observations**
**High Altitude Water Cherenkov (HAWC) future**

## High Energy Particle Astrophysics

** ****What do we know?**
- Nature accelerates particles to >1020 eV
- Gamma-ray sources accelerate particles to >1014 eV
** ****What do we want to know?**
- What astrophysical sources accelerate particles?
- How do astrophysical sources accelerate particles?
- What new high energy physics can we learn from astrophysics?

## Producing Gamma Rays: Astrophysical Particle Accelerators

**Producing Gamma Rays: ****Astrophysical Particle Accelerators**

- Black Hole producing relativistic jet of particles

- Massive Star Collapsing into a Black Hole

- SuperComputer Calculation

- Chandra Image of Crab

- HESS TeV
- + x-ray

- TeV image of Vela Jr. Supernova Remnant

## High Energy Particle Astrophysics

_**What tools do we use?**_
- Auger and HiRes measure the  highest energy cosmic ray flux, spectrum, and anisotropy
- ICECube searches for TeV neutrino sources – the most direct signature of hadronic accelerators
- GLAST will detect thousands of new GeV sources
- VERITAS, HESS, MAGIC, and CANGAROO image and measure spectra and variability of TeV sources
- Milagro’s images cosmic rays interactions in our Galaxy and searches for new and transient      TeV sources

## Detecting -rays from Satellites (30 MeV to 300 GeV -rays)

- -rays interact via pair production
- Background of cosmic rays is rejected by anticoincidence shield AND clear pattern of electron-positron pair

***-ray Interaction Cross Section*

## Satellite -ray Observatories >30 MeV

- Pre Compton Observatory
- SAS2
- CosB
- EGRET on the Compton Gamma-Ray Observatory
- 1991-2000
- Fermi Gamma-Ray Space Telescope (GLAST)
-  June 2008-2018

**Notes:**
Sas2 cosb dates.  CGRO picture EGRET yellow picture

## Detecting -rays from the Ground (>~50 GeV) 

- Extensive Air Showers (EAS) of relativistic particles are created when -rays and cosmic-rays impact Earth’s Atmosphere
- Relativistic Particles in EAS emit light
- Cherenkov Light
- 	Exceeding the wave speed in a medium produces a shock wave (similar to sonic boom)
- Cherenkov angle in air is ~1o
- Cherenkov angle in water is ~ 40o

- Cone of
- light

## Simulation of 2 TeV -ray in Atmosphere 

## Simulation of 2 TeV Proton in Atmosphere

## Comparison of Gamma-Ray Detectors 

- _Large Aperture/High Duty Cycle_
- Milagro, Tibet, ARGO, HAWC

**Moderate Area **
**Good Background Rejection**
**Large Duty Cycle/Large Aperture**

**Unbiased Sky Survey **
**Extended sources**
**Transients (GRB’s) **
**Solar physics/space weather**

_**Milagro Gamma Ray Observatory **_
_**@ 8600’ altitude near Los Alamos, NM**_

**A. Abdo, B. Allen, D. Berley, T. DeYoung,B.L. Dingus, R.W. Ellsworth, M.M. Gonzalez, J.A. Goodman, C.M. Hoffman,P. Huentemeyer, B. Kolterman, J.T. Linnemann, J.E. McEnery, A.I. Mincer, P. Nemethy, J. Pretz, J.M. Ryan, P.M. Saz Parkinson, A. Shoup, G. Sinnis, A.J. Smith, D.A. Williams, V. Vasileiou, G.B. Yodh**

## How Does Milagro Work?

- Detect Particles in Extensive Air Showers from Cherenkov light created in 60m x 80 m x 8m pond containing filtered water
- Reconstruct shower direction to ~0.5° from the time different PMTs are hit
- 1700 Hz trigger rate mostly due to Extensive Air Showers created by cosmic rays
- Field of view is ~2 sr and the average duty factor is >90%

## Inside the Milagro Detector

## Array of 175 Outriggers

- 8’ dia. x 3’ deep

- Pond Area is 3600 m2 operational in January 2001
- Outrigger Array area is ~ 30000 m2 operational in June 2004

## Curvature Correction

**Curvature Correction**

- The shower front is not a plane, but is curved about the shower core
- Times of individual PMTs are adjusted based on the distance to the shower core

- Core Location Error vs
- True Core Distance from Center of Pond

- Without Outriggers

- With Outriggers

- Core Distance (meters)

- Core Distance (meters)

- Core Error (meters)

- Core Error (meters)

- Curved Shower Front
- 7ns/100m

## Moon for Monitoring

- Cosmic Rays are Shadowed by the Moon (0.5o dia.)
- Shadow is deflected by Earth’s magnetic field at low energies
- Deflection measures Milagro’s energy scale for protons
- Shadow size measures Milagro’s angular resolution for protons

- Moon Shadow in direction with minimum deflection by Earth’s B

## Background Rejection in Milagro

- Use bottom layer of Milagro to detect penetrating particles (primarily muons) which are more prevalent in cosmic-ray (hadronic) showers than gamma-ray (electromagnetic) showers

**Notes:**
*When a gamma event core falls on the pond, a lot of energy falls in a small region of the pond, making the event look proton-like, in turn making gamma-hadron separation difficult for these types of events, even though the angular resolution is good
*easier to separate gammas from hadrons for cores falling off the pond, but without ORs, the angular resolution is worse than events falling on the pond
=>ORs have improved off-pond ang res

## Milagro Observation in Galactic Coordinates

**Crab Nebula**

**Cygnus Region**

## Abdo, et al. ApJ 2007

- Milagro has discovered 3 new sources & 4 candidate sources in the Galaxy.
- 5/7 of these TeV sources have GeV counterparts (only 13 GeV counterparts in this region - excluding Crab)
- Probability = 3x10-6

## The Cygnus Region

**The Cygnus Region**

- MGRO J2019+37: 10.9σ
- Extended source 1.1o ± 0.5o (top hat dia.)
- Possible Counterparts
- GeV J2020+3658, PWN G75.2+0.1
- MGRO J2031+41: 6.9σ (5.0σ post-trials)
- Possible Counterparts:
- 3EG J2033+4118, GEV J2035+4214
- TEV J2032+413 (1⁄3 of Milagro flux)
- 3.0o ± 0.9o (top hat dia.)
- C1 J2044+36: 5.5σ pre-trials
- no counterparts
- < 2.0o
- C2 J2031+33: 5.3σ pre-trials
- no counterparts
- possible extension of MGRO J2019+37
- possible fluctuation of MGRO J2019 tail & diffuse emission & background
- Tibet AS preliminary detections of 3 sources

- Abdo, et al. ApJ 2007
- Wang, et al. ICRC 2007

##  Diffuse Emission

- Cygnus Region with Matter Density Contours overlaying Milagro Significance
- Source Subtracted Longitude Profile

- Abdo et al ApJ Lett 2007

## Galactic Diffuse Emission (Spatial Distribution)

- Cygnus Region
- 65o<longitude<85o

- Inner Galaxy
- 30o<longitude<65o

- GALPROP Model
- o decay Inverse Compton Total

- GALPROP Model
- o decay Inverse Compton Total

- Inverse Compton target photons extend to higher latitudes
- Pion decay due to interactions with matter at low latitudes
- Inverse Compton flux increases towards inner Galaxy
- HAWC’s flux error bars will be ~10 x smaller than Milagro’s
- Plots show Milagro flux after subtracting 8 Milagro detected sources.  IACT surveys will allow further improvement in source subtraction.

- /TeV/cm2/sr/sec @ 15 TeV

- /TeV/cm2/sr/sec @ 15 TeV

## Galactic Diffuse Emission

- 	Expect Spectral Differences vs Galactic Longitude

**GALPROP Conventional (solid) and **
**Optimized (dashed) Models**

- 65o < l < 85o
- |b| < 2o

- 30o < l < 65o
- |b| < 2o

**Milagro**
** ****Obs.**

**Inverse Compton Scattering**
**	****CMB**
**	****Dust**
**	****Starlight**
**Pion Decay**
- Extragalactic Background
**Brems.**

## Introduction of Energy Parameter

- Parameter Range: 0.2-2. in 9 bins

## Energy Dependence of FrASOR

- 0.2-0.4

- 1.0-1.2

- 1.8-2.0

- Energy resolution is dominated by shower fluctuations.

## Energy Dependence of FrASOR

## Crab spectrum: Power Law Fit with Exponential Cutoff

- χ2 = 3.86 (6 dof)

- α = 3.08

- I0(E/1TeV)= 8.65 x 10-7 m-2 s-1Tev-1

- Ecut = 251 TeV

## Crab spectrum: Power Law Fit with Exponential Cutoff

## MGRO 1908+06 Spectrum

- χ2 = 3.1 (6 dof)

- α = 1.62

- Ecut = 20 TeV

- I0(E/1TeV)=
- 8.19 x 10-8 m-2 s-1Tev-1

## Systematic Check: Fitting the Cosmic Ray Spectrum

- Verify Stability of Detector

*4 years*

- Change in Spectral Index

- Change of Normalization

## From Milagro to HAWC

- Increase Altitude to 4100 m from 2650 m
- Increase Area to 22,000 m2 from 4,000 m2 (top layer) or 2,200m2 (bottom layer)
- Reuse 900 Milagro PMTs and front end electronics
- Equipment Cost $7.4M
- HAWC 10 – 15 x Sensitivity of Milagro:
- HAWC: Detect Crab in ~ 1 day (5)
- Milagro: Detects Crab in 3 months

## HAWC Detector Design

- 900 water tanks
- One 8” PMT/tank
- Tank array covers area of 150m x 150m with 78% coverage

**DAQ trailer**

**Road**

**HAWC Tank Array in GEANT 4**

## Tanks vs Pond

**Tanks vs Pond**

- Less expensive
- Build incrementally
- Expandable & upgradeable

_**GEANT4 Simulation**_
- Muon (thinned 1/50) produces up to 100s of pes depending on impact parameter

- 100 MeV ray (thinned 1/200) produces 1pe/60 MeV *independent* of impact parameter

## Site Location is Sierra Negra, Mexico

- 4100 m above sea level
- Latitude of 19 deg N
- Easy Access
- 2 hr drive from Puebla
- 4 hr drive from Mexico City
- Existing Infrastructure
- Few km from the US/Mexico Large Millimeter Telescope
- Power, Internet, Roads
- Sierra Negra Scientific Consortium of ~7 projects
- Excellent Mexican Collaborators
- ~15 Faculty at 7 institutions have submitted proposal to CONACYT for HAWC
- Experience in HEP, Auger, and astrophysics (including TeV)

## HAWC Collaboration

**USA:****	**
_**Los Alamos National Laboratory**__** **_**Brenda Dingus,  Gus Sinnis, Petra Huntemeyer, John Pretz**
_**University of Maryland**__** **_**Jordan Goodman, Andrew Smith, Vlasios Vasileiou, Greg Sullivan**
_**University of Utah**__** **_**Dave Kieda**
_**University of New Mexico**__** **_**John Matthews**
_**Michigan State University**__** **_**Jim Linnemann**
_**Pennsylvania State University**__** **_**Ty DeYoung**
_**NASA/Goddard Space Flight Center**__** **_**Julie McEnery**
_**University of New Hampshire**__** **_**James Ryan**
_**University of California, Irvine**__** **_**Gaurang Yodh**
**Mexico:****	**
_**Instituto Nacional de Astrofísica Óptica y Electrónica (INAOE)**__** **_
**	****Alberto Carramiñana, Eduardo Mendoza**
_**Universidad Nacional Autónoma de México (UNAM)**_
**	**_**Instituto de Astronomía:**_** Magdalena González, Dany Page, William Lee, Hector Hernández, Deborah Dultzin, Erika Benitez**
**	**_**Instituto de  Física**_**: Arturo Menchaca, Rubén Alfaro, Andres Sandoval, Ernesto Belmont **
**	**_**Instituto de Ciencias Nucleares**_**: Lukas Nellen, G. Medina-Tanco**
**	**_**Instituto de Geofísica**_**: José Valdés Galicia, Alejandro Lara**
_**Benemérita Universidad Autónoma de Puebla**_** **
**	****Humberto Salazar, Oscar Martínez, Cesar Álvarez, Arturo Fernández**
_**Universidad Michoacana de San Nicolás de Hidalgo**__** **_**Luis Villaseñor**
_**CINVESTAV **_**Arnulfo Zepeda**
_**Universidad de Guanajuato**_
**	****David Delepine, ****Gerardo Moreno, Marco Reyes, Luis Ureña****, Victor Migenes**

## HAWC Sensitivity is 15x Better than Milagro’s

- e

- 

- 

- Larger Effective Area at Lowest Energies
- Better Angular Resolution
- Improved Background Rejection
- => 10-15 x improvement in flux sensitivity
- => (10-15)2 = 100-200 x faster to observe same flux

- 100 GeV           1 TeV          10TeV     100 TeV

- 100 GeV           1 TeV          10TeV     100 TeV

- Hadron Efficiency         Ang. Res. (deg)              Eff. Area (m2)

- 100 GeV           1 TeV          10TeV     100 TeV

- 100 GeV           1 TeV          10TeV     100 TeV

## Higher Altitude is Closer to Shower Max.

- 4500m

- 2600m

- Difference between 2600m (Milagro) and 4100m (HAWC):
- 	~ 5x number of particles
- 	~ 2x lower energy threshold

**Higher Altitude is Closer to Shower Max.**

## Lateral Distribution of Extensive Air Showers

- Gammas have NARROW lateral distribution of electrons
- Protons have BROAD lateral distribution of muons

**Lateral Distribution of Extensive Air Showers**

## Gamma/Hadron Separation

**Gamma/Hadron Separation**

- Size of HAWC

- Size of Milagro deep layer

- Energy Distribution at ground level

- Rejection factor ~ e-<>

## Sensitivity to Crab-like (dN/dE=E-2.6) Point Source 

- E F(>E) (TeV/cm2s)

**Sensitivity to Crab-like (dN/dE=E****-2.6****) Point Source **

- GeV

**HESS/VERITAS,**** ****MAGIC****, ****Whipple, ****CTA **sensitivity in 50 hours, (~0.2 sr/year)
**GLAST** sensitivity in 1 year (4 sr)
**HAWC **sensitivity in 1(5) years shown as solid (dashed) line (2 sr)
- HAWC sensitivity at high energies is conservatively estimated because no MC cosmic rays pass the gamma ray cut.
- HAWC exposure          >10 TeV in 5 years is 5x1015 cm2sec =               1 km2 x 140 hrs

## HAWC’s Field of View

- = 2.6sr
- = 1.8  sr

## HAWC Science Objectives

- Constrain the** **origin of cosmic rays** **via** **HAWC’s observations of -rays up to 100 TeV**  **from discrete sources and the Galactic plane.
- Probe** **particle acceleration** **in extreme magnetic and gravitational fields via** **HAWC’s observations of transient TeV sources**, **such as gamma ray bursts and supermassive black holes.
- Explore new TeV physics via HAWC’s unbiased sky survey with a detection threshold of ~30 mCrab in two years.** **

## HESS J1616-508

**HESS J1616-508**
**0.2 Crab @ 1 TeV ********=-2.3****Highest energy ****~20 TeV**

## HESS J1616-508

**HESS J1616-508**
**0.2 Crab @ 1 TeV ********=-2.3****Highest energy ****~20 TeV****Simulated HAWC data for 1 year with no cutoff**

## HESS J1616-508

**HESS J1616-508**
**0.2 Crab @ 1 TeV ********=-2.3****Highest energy ****~20 TeV****Simulated HAWC data for 1 year with 40 TeV exponential cutoff**

## Cosmology from EBL Absorption 

**Cosmology from EBL Absorption **

- HESS & MAGIC constraints on the EBL require the intrinsic spectrum of AGN is very hard
- HAWC will increase the # of sources & the # of flares from the same source to decouple source dependent effects
- Highest Energy Spectra constrains longest wavelength EBL
- HAWC’s Spectra to > 10 TeV measures the dust temperature & impacts Galaxy Formation theories

- GLAST

- IACT

- HAWC

## Extragalactic Science: HAWC & Transients

- GLAST and HAWC sensitivity for a source of spectrum
- dN/dE=KE-2
- z=0	no E cutoff
- z=0.1	Eexp~700GeV
- z=0.3	Eexp~260GeV
- z=0.5	Eexp~170GeV

- 10-12

- 10-10

- 10-8

- 10-6

**TeV AGN flares**

**GRB **
**<1 MeV**

- AGN and GRBs have bright flares
- e.g. PKS J2155-304 (z=0.117) flared to 50x quiescent flux in one hour with dN/dE=kE-3.5 which would give 6  in HAWC

## AGN Monitoring

**AGN Monitoring**

- HAWC will obtain duty factors and notify multiwavelength observers of flaring AGN in real time.
- All sources within ~2  sr would be observed every day for ~ 5 hrs.
- HAWC’s continuous observations would not have gaps due to weather, moon, or solar constraints.
- HAWC’s 5  sensitivity is (10,1,0.1) Crab in (3 min, 5 hrs, 1/3 yr)

- Worldwide Dataset of TeV Observations by IACTs of Mrk421

- 1 month

## AGNs

- HAWC will obtain duty factors and notify multiwavelength observers of flaring AGN in real time.
- Milagro has observed 7yr lightcurve of Mrk 421
- HAWC’s increased sensitivity would result in ~10x smaller error bars and have similar error bars on hour time scale rather than 64 days

- Milagro - Events/day

- ASM Flux cts/s

- MJD - 50000

**Milagro and ****XTE ASM**** 7 yr lightcurve of Mrk 421 **
**(Smith et al. ICRC 2007)**

## Discovery Potential with Unbiased Survey

**Discovery Potential with Unbiased Survey**

- Known TeV source classes, such as x-ray binaries and microquasars
- HAWC will monitor for flares and for periods difficult for IACTs
- Postulated TeV source classes, such as Galaxy Clusters & GLAST sources
- HAWC’s field of view contains 100s of Galaxy Clusters within z<0.1
- >1/2 of GLAST sources will be within HAWC’s field of view

- HESS x-ray binary obs. & HAWC’s sensitivity

## Expect the Unexpected

**Expect the Unexpected**

- Milagro Observes Anisotropy in 10 TeV Cosmic Rays
- 10 deg size scale with a fractional excess of 7e-4 above the cosmic ray background (15 )
- Excess is not gamma rays, but charged cosmic rays (7 )
- Largest excess is not consistent with the locally measured cosmic ray energy spectrum (4 , but is harder with a cut off of ~10 TeV
- Explanations are difficult because the gyroradius of a 10 TeV proton in a 1 G field is 0.01 parsecs=2000 AU
- Maybe Geminga SNR??? Salvati & Sacco astroph0802.2181
- Requires unexpected order in magnetic field (Drury & Aharonian 2008)

- Heliotail

- Geminga

- Galactic
- Plane

## Conclusion

- Milagro has demonstrated success of the water Cherenkov technique
- Discovery of TeV emission from the Galactic plane
- Image of TeV emission from the Cygnus region
- 7 New Candidate TeV Sources
- Future Plan is HAWC
- Building on expertise with Milagro
- Design improvements in Size, Altitude, Curtains . . .
- >10x Milagro sensitivity
- HAWC is Synergistic Component of Particle Astrophysics Portfolio
- Gamma-rays point back to astrophysical accelerator
- Identify which of GLASTs 1000s of sources extend to TeV energies and monitoring these sources daily
- Determine targets for the Atmospheric Cherenkov Telescopes to use their enhanced angular and energy resolution
- Improve IceCube sensitivity by identifying flaring sources

## TeV -rays: A New Window on the Sky

**0.1 GeV**

**Milagro 10 TeV gamma-ray**

## Funding Status

- October 2007: NSF proposal submitted for $7.4M equipment funds for HAWC
- December 2007: NSF panel review states “There is a strong case for HAWC as a wide field of view survey instrument at the TeV scale.” They concluded the project is well understood and technically ready with a strong collaboration.
- August 2008:  NSF Major Research Instrumentation (MRI) HAWC development proposal funded for $1M.
- Mexican CONACyT funding is also being sought.  For example, HAWC is a major part of the High Energy Physics Megaproject which has $1M this year.

## Nearby AGN

**Nearby AGN**

- M87 is a known, variable source of TeV -rays
- HAWC will detect average flux at 5.8extending spectra to highest energies & monitoring variability
- Auger’s evidence for a correlation of UHECR with AGN point to other nearby particle accelerators
- UHECR directions are deflected by several degrees, so individual sources can’t be determined
- However, UHECR will produce TeV gamma-rays near the sources due to interactions with the CMB & infrared
- HAWC can search the 100s of nearby AGN to find UHECR emitters

- Auger’s 27 UHECRs (black circles) > 6e19eV & nearby, z<0.018, AGN (red *) plotted in Galactic coordinates with the SuperGalactic plane indicated by the dashed line

## GeV Galactic Diffuse Spectrum

- NN: cosmic-ray nucleon + nucleus -> o + ...-> s
- EB: cosmic-ray electron bremstrahlung
- IC: inverse Compton scattering of cosmic-ray electron on IR or CMB
- ID: isotropic diffuse -rays of unknown origin

- Hunter et al. ApJ (1997)

- GeV Excess

- de Boer et al.  A&A (2005)

- GeV Excess Explanations:
- 1) Dark Matter

- 2) Cosmic Ray flux near Earth is low

- Strong et al. ApJ (2004)

- 3) ???

## TeV Galactic Diffuse Spectrum

- GALPROP model of the cosmic ray production, propogation, matter, and radiation fields in the Galaxy
- Strong *et al*., *ApJ* **613**, 962 (2004)
- Strong *et al*., *A&A* **422**, L47 (2004)
- “Conventional” model uses local cosmic-ray flux
- “Optimized” model increases cosmic-ray flux to match EGRET
- Milagro flux exceeds GALPROP predictions
- BUT are there unresolved sources???

## Gamma Ray Bursts & Other Transients

- Milagro data searched within 4 seconds for transients.
- Time intervals searched vary from milliseconds to weeks.
- No significant excess has been detected.
- Constrains TeV emission from Gamma-Ray Bursts for an assumption of the redshift distribution of sources and the luminosity distribution

- Distribution of probabilities for a typical day’s observations of one time interval

## Milagrito Evidence for TeV GRB

- Milagrito operated ~ 1 year during the BATSE era
- 54 GRBs within fov
- GRB 970417a
- Weak BATSE GRB with poor localization
- Milagrito detection had a post-trial chance probability of 1.7x10-3 (including the 54 bursts searched and the large location uncertainty).
- TeV fluence > 10x keV fluence

- Redshift unknown so TeV flux emitted is uncertain.

- GRB970417a

## Milagro Searches for GRB Satellite Notifications

- No GRBs detected but satellite detections in fov have been rare
- Milagrito: ~ 54 GRB/year
- 2002-2004: ~ 4 GRB/year
- Since SWIFT launch ~ 100 GRBs, but avg redshift > 2
- TeV -rays are absorbed by extragalactic IR photons, so z<0.3 is needed to make constraining measurement

- _Interesting Bursts_
- GRB010921, z=0.45
- Eiso(TeV)/Eiso(keV) < 1-4 (depending on EBL model)
- Atkins et al 2005 ApJ
- GRB 041219:
- long (520s)
- bright (1x10-4 erg cm-2)
- Gal Lat=0
- If z=0.1-0.5 =>Eiso(TeV)/Eiso(keV) < 0.3 - 7
- GRB 050509b
- short/hard burst
- Weak (2x10-8 erg cm-2)
- z=0.225?
- GCN Circular 3411
- Eiso(TeV)/Eiso(keV) < 10 – 20 (depending on EBL model)
- ~20 short duration bursts within Milagro’s field of view

- GRB010921, z=0.45
- Eiso(TeV)/Eiso(keV) < 1-4
- (depending on IR model)

- Satellite data

- Milagro data

## Solar Physics

- Coronal mass ejections are an ideal laboratory to study particle acceleration
- By monitoring the singles rates in all PMTs we are sensitive to “low”-energy particles (>10 GeV)
- Milagro has detected 4 outbursts from the Sun with >10 GeV particles

## X7-Class flare Jan. 20, 2005

- GOES proton data
- >10 MeV
- >50 MeV
- >100 MeV

- Milagro scaler data
- > 10 GeV protons
- ~1 min rise-time
- ~5 min duration
- inset 2 min grid

- Milagro PMT Rates

## Forbush Decreases – The interplanetary field

## Absorption of TeV Photons

- e+

- e-

- ~eV 

- ~TeV 

## GeV Sources Emit TeV Gamma-Rays

**Abdo, et al. ApJ Lett 2007**

**GeV Sources Emit TeV Gamma-Rays**

- Milagro has discovered 3 new sources & 4 candidates in the Galaxy.
- 5/7 of these TeV sources have GeV counterparts.
- Only 13 GeV counterparts in this region - excluding Crab. Probability = 3x10-6

**LS I + 61 303**

**HESS J0632+057**

**IC443**

**H**

**H**

- HAWC+GLAST will survey the sky from 100 MeV to 100 TeV.

## Galactic Sources are Extended

**Galactic Sources are Extended**

- EAS ~0.5o IACT ~0.1o
- HAWC’s large fov of 2 sr:
- Entire source & background are simultaneously observable
- Background is well measured

## Active Galactic Nuclei

- Open questions
- Protons or electrons?
- Plasma Bulk Lorentz factor?
- B-field?
- Location of -ray production?
- Acceleration mechanism?
- HAWC observations
- Many flares from known TeV AGN
- New TeV AGN
- Spectra > 1 TeV
- Multiwavelength Observations with other wide field observatories & by rapid notification

## HAWC sample GRB lightcurve

- High Energy cut off could occur due to absorption in GRB or in transit via EBL interaction.
- Measurements of lightcurve reveal information about progenitor and constrains Lorentz invariance.

- HAWC lightcurve of a bright GRB (1e-4 ergs/cm2 fluence). Weaker burst counts scale with fluence.

## Milagro technique works
Discovery of diffuse TeV gamma rays from Galactic plane & Cygnus region
Discovery of new Galactic TeV sources 
Demonstration of long-term multi-wavelength AGN monitoring
Unexpected TeV Cosmic-ray anisotropy observed
With HAWC Large improvements are possible 
10-15 times the sensitivity of Milagro 
~5 /√day on the Crab
3% of Crab flux sensitivity over entire hemisphere (after 2 year operation)
Scientific Capabilities
Highest energies 
Extended sources
Galactic diffuse emission
TeV transients 
Unbiased Sky survey

- Discovery of diffuse TeV gamma rays from Galactic plane & Cygnus region
- Discovery of new Galactic TeV sources
- Demonstration of long-term multi-wavelength AGN monitoring
- Unexpected TeV Cosmic-ray anisotropy observed
- With HAWC Large improvements are possible
- 10-15 times the sensitivity of Milagro
- ~5 /√day on the Crab
- 3% of Crab flux sensitivity over entire hemisphere (after 2 year operation)
- Scientific Capabilities
- Highest energies
- Extended sources
- Galactic diffuse emission
- TeV transients
- Unbiased Sky survey

**Conclusions**

## Milagro Observation in Galactic Coordinates

**Crab Nebula**

**Cygnus Region**

## Crab

- Nebula

- Mrk 421

- 7 year data set (July 2000-July 2007)
- Weighted analysis using A4 parameter
- Best data from 2004 on with outriggers
- Crab nebula 15 
- Galactic plane clearly visible

- Cygnus
- Region

## GRBs

- Milagro searches data within few seconds for short duration transients and sends alerts to GCN, but has found no significant emission
- HAWC’s low energy response allows dimmer GRBs at more distant redshifts to be observed

## Shower Fluctuations Dominate Energy Resolution
Higher Altitude of HAWC increases # of particles by ~6x 
Ability to measure a high energy cut off is a combination of the energy resolution AND the statistical error in the flux

- Higher Altitude of HAWC increases # of particles by ~6x
- Ability to measure a high energy cut off is a combination of the energy resolution AND the statistical error in the flux

**HAWC Energy Resolution**