VERITAS: Status and latest results

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VERITAS Status and latest results

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

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Outline

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

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The VHE Sky - 1995
g rays, 50GeV-50TeV
3 sources
Mrk421
Mrk501
Crab
R.A.Ong Sep 2005
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The VHE Sky - 2003
12 sources
Mrk421
H1426
M87
Mrk501
1ES1959
RXJ 1713
Cas A
GC
Crab
TeV 2032
1ES 2344
PKS 2155
R.A.Ong Sep 2005
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The VHE Sky - 2007
gt50 sources
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VHE g-ray Science
SNRs
Gamma-Ray Bursts
Origin of Cosmic Rays
Pulsars
Microquasars
Testing Lorentz Invariance
?
AGN
Cold Dark Matter
cosmological g-Ray Horizon
Something New !
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Major New VHE Telescopes
MAGIC
MILAGRO
(Auger, CRs)
IceCube, ns (2011)
HESS
CANGAROO
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Cherenkov Telescopes
g-ray
g/hadron separation
p
g
20 km
q 1.5o
1.4 km
Collection area 105 m2
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Cherenkov Telescope Arrays
2
Stereoscopic viewing
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VERITAS
Very Energetic Radiation Imaging Telescope
Array System (VERITAS)
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VERITAS Collaboration 80 members in more than
20 institutions

• 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
Funding from NSF/DOE/Smithsonian/PPARC/SFI/NSERC
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VERITAS
VERITAS-4 at the Whipple Observatory
F.L. Whipple Basecamp Mt. Hopkins, AZ (1300m
a.s.l.)
Spring 2007
T4
T1
T3
T2
Since January 2006
Fall 2006
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Telescope and Camera
499 PMTs (Photonis XP 2970/02) 0.15o pixel
separation, 3.5o FOV
12m reflector, f1.0 optics
499 pixel Camera
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VERITAS Data Acquisition

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

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VERITAS Trigger System
Level One Pixel
3-telescope array
Level Two Camera (NSB)
Array
Single-telescope
Another advantage of stereo!
Dependence of the array trigger (L3) and pattern
trigger rates (L2) on CFD (L1) thresholds
Level Three Array (muons, NSB)
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Supernova Remnants
Supernova Remant (Shell)
Pulsar Wind Nebula/Plerion

• And composites
• Probable source of cosmic rays up to the knee
  (1015 eV)
• Morphology, multi-wavelengthacceleration sites

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Old Friends
Mrk421
Mrk501
Crab
Calibration source
R.A.Ong Sep 2005
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VERITAS Performance
angular resolution
off-axis sensitivity

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

• off-axis sensitivity gt50 for source offsets lt 1o

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Old friends Crab Nebula
Energy spectrum
1 Crab 100s (5s) 10 Crab 1 hr 3 Crab
10 hrs

• 2 telescope array G-2.550.03, F(Egt1
  TeV)(3.10.06)x10-7 m-2s-1
• 3 telescope array G-2.430.05, F(Egt1
  TeV)(3.10.16)x10-7 m-2s-1

• significance 30 s/vhour for three telescope
  array (7 ?/min)

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Detection of Supernova Remnant IC 443
IC 443
EGRET source (overlaps remnant)
Figures from Torres et al. Phys. Rep. 382, 303
(2003) MAGIC point from Albert et al.
astro-ph/0705.3119v1
Crab Nebula
MAGIC source (first detection in VHE) overlaps
cloud (target material)

• Results consistent with MAGIC 5.7 s detection in
  29 hrs

• VERITAS observation/detection
• 16 hours of data (3-tel. array)
• 7.1 s pre-trials, 6.0 s post-trials
• Flux F(Egt200 GeV) 3 Crab Flux

• position agrees with interaction zone of
  molecular cloud

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LS I 61 303 ?-rays from a binary

• 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 s (confirms
  MAGIC discovery)

significance
significance
moonlight
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LS I 61 303 continued
energy spectrum
contemporaneous TeV and X-ray data
orbital phase 0.5-0.8
October 2006
PRELIMINARY

• 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

• power law G -2.6
• maximum flux corresponds to about 10 of the flux
  of the Crab Nebula

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AGN Detections

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

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More old friends Mrk421 Mrk501
2 telescope data

• Mrk421
• 17 hours of observations (April 2006, 2
  telescopes)
• 35s detection
• Active phase

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

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VERITAS 1ES 1218304
Raw rates (no zenith angle correction)

• Third furthest VHE blazar (z0.182)
• 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 s, 0.230.03 ?/min
• No indication of variability
• still need to correct for zenith angle dependence

constant flux fit ?211.21/11
March 2007
February 2007
January 2007
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Extragalactic objects M87

• 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
  ?-rays
• HEGRA 4.1 s (1998-1999)
• HESS 13 s (2003-2006)
• variable on different time scales
• 2 day-scale variability during M87 high state
  (2005)

http//www.aoc.nrao.edu/fowen/M87_layout.html
VLA Image 20cm
Chandra X-ray
HST Optical
VLA Radio
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VERITAS M87

• Observation
• 44 h with 3-telescope array
• 5.1 s, Rate of 0.1 ?/min
• 1.7 of Crab Nebula flux (Egt250 GeV)

• No statistically significant variability

?2-distribution
light curve
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10
constant flux fit ?221.4/22
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6
Flux ( of the Crab Nebula)
4
2
0
?2 deg2
February 2007
March 2007
April 2007
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Key Science Projects
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VERITAS Sky Survey

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

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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)

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Summary

• VERITAS is now operational!
• Sensitivity of 10 of Crab Nebula flux in lt 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

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EXTRA/ BACKUP
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VERITAS Trigger System
Level Two
Shower Delay ( 1 PDM channel per trigger signal)
Pattern Trigger
(x4 1 per telescope)
Array Trigger Coincidence Logic (SAT Board)
Event Decision
Event Logic Inhibitor
FADC Modules (1 channel per pixel)
Event Information
FIFO Buffer
64µs circular buffer
Serialized Event Information
Readout instructions
L3 Trigger
Compensating Delay ( 1 PDM channel per trigger
signal)
Telescope Data Acquisition System
Harvester Process
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Trigger System Performance
3-telescope array
Array
Single-telescope
Another advantage of stereo!
Array dead time a array rate (typical array
rate 220Hz, dead time 10) Dominated by data
acquisition
Dependence of the array trigger (L3) and pattern
trigger rates (L2) on CFD (L1) thresholds
? Partial moonlight capability (still under
study)
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The difference of stereo- early VERITAS data
Single telescope trigger threshold
150GeV Single telescope analysis threshold
400GeV
muon peak
muon ring
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Typical Gamma-ray event
Reconstruction of ?-ray direction
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LS I 61 303
from Mirabel (Science 309, 714, 2006)
Two models for high-energy emission
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Other observations (UL)

• SNR/PWN upper limits
• J20213651, J22296114, J02056449 (3C58) at 2-5
  of the Crab Nebula flux
• Gamma-ray burst upper limits
• GRB 070311, 070521, 070612
• Blazar/AGN upper limits
• 1ES 0647250, 1ES 0806524, 3C279, ..

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VERITAS Science Program
Bulk Program 40
Discretionary 10

• Key Science Projects
• Four highlight science topics.
• Bulk Science Program
• All possible topics.
• Determined by TAC selection.
• Discretionary Time
• ToOs, unique topics, engineering.
• Determined by Spokesperson.

Key Science Projects 50
40
Sky Survey Observation Scheme