# Presentation: 536301

## VERITAS: Status and latest results

- Amanda Weinstein
- for the VERITAS Collaboration
- International Symposium on Multiparticle Dynamics,
- Aug. 7, 2007

## Outline

**Background and Motivation**
**Atmospheric Cherenkov Telescopes**
**The VERITAS project**
- Description, operation, performance
- Early results
- Science Program
**Summary**

## The VHE Sky - 1995

**Mrk421**

**Mrk501**

**Crab**

**R.A.Ong**
**Sep 2005**

- 3 sources

-  rays, ~50GeV-~50TeV

## The VHE Sky - 2003

**Mrk421**

**H1426**

**Mrk501**

**1ES1959**

**1ES 2344**

**PKS 2155**

**Cas A**

**RXJ 1713**

**Crab**

**TeV 2032**

**M87**

**GC**

**R.A.Ong**
**Sep 2005**

**The VHE Sky - 2003**

- 12 sources

## The VHE Sky - 2007

**The VHE Sky - 2007**

- >50 sources

## VHE -ray Science

- SNRs

- Cold Dark Matter

- Pulsars

- Gamma-Ray
- Bursts

- cosmological
- g-Ray Horizon

- AGN

- Origin of Cosmic
- Rays

- Microquasars

- Testing Lorentz Invariance

- Something New !

- ?

## Major  New VHE Telescopes

**MAGIC**

**HESS**

**CANGAROO**

**(****Auger****, CR’s)**

**IceCube, ****n’s**** (2011)**

- MILAGRO

## Cherenkov Telescopes

******-ray**

******~ 1.5****o**

-       **Collection area ~ 10****5**** m****2**

****/hadron separation

****

**20 km**

**1.4 km**

**p**

## Cherenkov Telescope Arrays

- 2

**Cherenkov Telescope Arrays**

**Stereoscopic viewing**

## VERITAS

**Very Energetic Radiation Imaging**
**    ****Telescope Array System**
**(VERITAS)**

## VERITAS Collaboration 

** ****Smithsonian Astrophysical Observatory ***
** ****Adler Planetarium**
** ****Purdue University ***
** ****Barnard College, NY**
** ****Iowa State University ***
** ****DePauw University, IN**
** ****Washington University, St. Louis ***
** ****Grinnell College, IA**
** ****University of Chicago ***
** ****University of California, Santa Cruz**

** ****University of Utah ***
** ****University of Massachussetts**
** ****University of California, Los Angeles ***
** ****Cork Institute of Technology**
** ****McGill University, Montreal ***
** ****Galway-Mayo Institute of Technology**
** ****National University of Ireland, Dublin ***
** ****National University of Ireland, Galway**
** ****University of Leeds ***
** ****Argonne National Lab**
**Associate Members **

**Project office: Whipple observatory SAO **

- VERITAS Collaboration
- ~80 members in more than 20 institutions

**Funding from NSF/DOE/Smithsonian/PPARC/SFI/NSERC**

## VERITAS 

**T1**

**T2**

**T4**

**T3**

**VERITAS **

- F.L. Whipple Basecamp
- Mt. Hopkins, AZ (1300m a.s.l.)

**Since**
**January**
**2006**

**Fall 2006**

**Spring 2007**

## Telescope and Camera

- 499 pixel Camera

- 12m reflector, f1.0 optics

- 499  PMTs (Photonis XP 2970/02)
- 0.15o pixel separation, 3.5o FOV

## VERITAS Data Acquisition

- PMTs digitized with 500 MS/s sampling FADCs
- 24 samples/channel/event

## VERITAS Trigger System

**VERITAS Trigger System**

- 3-telescope array

**Dependence of the array trigger ****(L3)**** and pattern trigger rates ****(L2)**** on CFD (L1) thresholds**

- Another advantage of stereo!

- Single-telescope

- Array

- Level One: Pixel

- Level Two: Camera (NSB)

- Level Three: Array (muons, NSB)

## Supernova Remnants

- Pulsar Wind Nebula/Plerion

**Supernova Remnants**

- And composites...
- Probable source of cosmic rays up to the “knee” (~1015 eV)
- Morphology, multi-wavelength...acceleration sites

## Old Friends

**Mrk421**

**Mrk501**

**Crab**

**R.A.Ong**
**Sep 2005**

- Calibration
- source

## VERITAS Performance 

**VERITAS Performance **

- angular resolution on event-by-event basis better than 0.14o (energy dependent)

- off-axis sensitivity >50% for source offsets < 1o

- angular resolution

- off-axis sensitivity

## Old friends: Crab Nebula

**Old friends: Crab Nebula**

- Energy spectrum

- 2 telescope array: Γ=-2.55±0.03, F(E>1 TeV)=(3.1±0.06)x10-7 m-2s-1
- 3 telescope array: Γ=-2.43±0.05, F(E>1 TeV)=(3.1±0.16)x10-7 m-2s-1

- significance ~30 σ/√hour for three telescope array (7 γ/min)

- 1 Crab       100s (5)
- 10% Crab  ~1 hr
-  3% Crab   ~10 hrs

##  Detection of Supernova Remnant IC 443

** ****Detection of Supernova Remnant IC 443**

**IC 443**

- VERITAS observation/detection
- ~16  hours of data (3-tel. array)
- 7.1 σ pre-trials, 6.0 σ post-trials
- Flux F(E>200 GeV) ~3% Crab Flux

- Crab
- Nebula

- EGRET source (overlaps remnant)

- MAGIC source (first detection in VHE)
- overlaps cloud (target material)

**position agrees with interaction zone of molecular cloud**

- Results consistent with MAGIC 5.7 σ detection in 29 hrs

- Figures from Torres *et al. *Phys. Rep. 382, 303 (2003)
- MAGIC point from Albert *et al.* astro-ph/0705.3119v1

## LS I +61 303: γ-rays from a binary

**LS I +61 303: **γ-rays from a binary

- significance

**HMXB:** Be-type star coupled with Neutron Star
-  VERITAS observation:
- 44 h of 2 and 3 telescope data **during ****5 orbital cycles**** covering phases 0.3-0.95**
**total detection significance: ****8.8 σ**** (confirms MAGIC discovery)**

- significance

**moonlight**

##                   LS I +61 303 continued

**                  ****LS I +61 303 continued**

- energy spectrum

-  power law Γ = -2.6
- maximum flux corresponds to about 10% of the flux of the Crab Nebula

- orbital phase 0.5-0.8

-  contemporaneous RXTE and Swift observations over 2 orbital cycles
- correlation between TeV and X-ray data (both SWIFT and RXTE)
- Sharper peak in gamma-rays

- contemporaneous TeV and X-ray data

- October 2006

- PRELIMINARY

## AGN Detections

- Active Galactic Nuclei
**High-luminosity extragalactic objects**
***Probe properties of the universe at large distances***
**Variable**
- AGN observed in VHE ****-rays are
**Mostly blazars**
*** ******Jets aligned with line of sight***
**Nearby: z < 0.19**

## More old friends: Mrk421 & Mrk501

-  **Mrk421**
- ~17 hours of observations (April 2006, 2 telescopes)
-  35σ detection
-  Active phase

-  **Mrk501**
- ~18.5 hours (April and June 2006, 2 telescopes)
-  Low state (not detectible by previous instruments)

- 2 telescope data

## VERITAS: 1ES 1218+304

-  **Third furthest VHE blazar (z=0.182)**
** ****EGRET source**
** ****Detected by MAGIC in VHE** (Albert et al. 2006)

**Exposure: 17.4 h of 2/3 telescope data**
** ****Zenith angle range = 2 to 35**
** ****9 σ, 0.23±0.03 γ/min**
** ****No indication of variability**
** ****still need to correct for zenith angle dependence**

- March 2007

- January  2007

- February 2007

- constant flux fit: χ2=11.21/11

-  Raw rates (no zenith angle correction)

## Extragalactic objects: M87

- http://www.aoc.nrao.edu/~fowen/M87_layout.html

-  **Giant radio galaxy**
** ****like a BL Lac, but jet does not point at us **
** ****jet seen in radio, optical and X-rays with similar morphologies **
- only extragalactic non-blazar object seen in VHE γ-rays
**	****HEGRA  4.1 **  **(1998-1999) **
**	****HESS  13 ** **(2003-2006) **
*** ******variable on different time scales***
*** ******2 day-scale variability during M87 high state (2005)***

- VLA Radio

- Chandra X-ray

- HST Optical

- VLA Image 20cm

## VERITAS: M87

**VERITAS: M87**

- θ2-distribution

- light curve

**Observation**
**44 h with 3-telescope array**
**5.1 σ, Rate of ~0.1 γ/min **
**~1.7% of Crab Nebula flux (E>250 GeV)**

- February 2007

- March 2007

- April 2007

- constant flux fit: χ2=21.4/22

- θ2 [deg2]

- Flux (% of the Crab Nebula)

- 12

- 10

- 8

- 6

- 4

- 2

- 0

** ****No statistically significant variability**

## Key Science Projects

## VERITAS Sky Survey

** ****2 year program: survey of Cygnus region ( -1 < b < 4 and 52 < l < 82 ) **
** ****Many targets of interest (SNRS, PWN, EGRET sources, X-ray binaries, VHE sources)**
** ****Survey started in late April 2007 (analysis ongoing)**

## Dark Matter KSP

- Dwarf galaxies
**Robust constraints  on DM content (allows constraints on particle physics models)**
**Observed 2 dwarf galaxies, Draco (~21h)& Ursa Minor (~23h), this past spring**
**Plan to observe 2-3 more in coming year**
- Sources with possibly enhanced central DM content (M31/M32/M33, M15)
**Limits are more speculative, but better chance of detection**

- Indirect detection of dark matter (e.g. SUSY neutralino annihilation)

## Summary

**VERITAS is now operational!**
- Sensitivity of 10% of Crab Nebula flux in < 1hr
- Broad scientific program
*Sky Survey*
*SNRs/PWN*
*Blazars*
*Dark Matter*
*Many others..*
- Early observations (construction/comissioning phase)
*Several interesting detections*
- Refinements/optimizations to come
- We are looking forward to next season

## EXTRA/

- BACKUP

## VERITAS Trigger System

**Pattern Trigger**

- Shower Delay
- ( 1 PDM channel
- per trigger signal)

- Array Trigger Coincidence Logic  (SAT Board)

- FIFO Buffer

- Compensating Delay
- ( 1 PDM channel
- per trigger signal)

- Event
- Decision

- Event
- Information

- Harvester Process

- Serialized Event Information

- L3 Trigger

** ****FADC Modules**
- (1 channel per pixel)

- (x4 : 1 per telescope)

**Readout **
**instructions**

- 64μs circular buffer

- Telescope Data
- Acquisition System

**Level Two**

- Event Logic
- Inhibitor

## Trigger System Performance

**Trigger System Performance**

**Array dead time**** ***α*** ****array rate **
**(typical array rate: 220Hz, **
**dead time ~10%)**
**Dominated by data acquisition**

- 3-telescope array

**Dependence of the array trigger (L3) and pattern trigger rates (L2) on CFD (L1) thresholds**

- → Partial moonlight capability
-  (still under study)

- Another advantage of stereo!

- Single-telescope

- Array

## The difference of stereo- early VERITAS data 

- muon
- peak

**The difference of stereo****- early VERITAS data**** **

- muon ring

- Single telescope
- trigger threshold ~150GeV
- Single telescope
- analysis threshold ~400GeV

**Notes:**
add Mrk421 theta-square plot.

## Typical Gamma-ray event

**Typical Gamma-ray event**

- Reconstruction of γ-ray direction

## LS I +61 303

**LS I +61 303**

- from: Mirabel (Science 309, 714, 2006)

- Two models for high-energy emission

## Other observations (UL)

**Other observations (UL)**

-  SNR/PWN upper limits
- J2021+3651, J2229+6114, J0205+6449 (3C58) at 2-5% of the Crab Nebula flux
- Gamma-ray burst upper limits
- GRB 070311, 070521, 070612
-  Blazar/AGN upper limits
-  1ES 0647+250, 1ES 0806+524, 3C279, ..

## VERITAS Science Program

- Key Science Projects:
**Four highlight science topics.**
- Bulk Science Program
**All possible topics.**
**Determined by TAC selection.**
- Discretionary Time
**ToO’s, unique topics, engineering.**
**Determined by Spokesperson.**

**Key Science Projects**
**50%**

**Bulk Program**
**40%**

**Discretionary**
**10%**

## Sky Survey Observation Scheme