Transcript VERITAS: Status and latest results

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
A. Weinstein
7 Aug 2007 – Berkeley
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The VHE Sky - 1995
g rays, ~50GeV-~50TeV
3 sources
Mrk421
Mrk501
Crab
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Pulsar Nebula
AGN
SNR
Other, UNID
7 Aug 2007 – Berkeley
R.A.Ong
Sep 2005
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The VHE Sky - 2003
12 sources
Mrk421
H1426
M87
Mrk501
1ES1959
RXJ 1713
Cas A
1ES 2344
TeV 2032
GC
Crab
PKS 2155
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Pulsar Nebula
AGN
SNR
Other, UNID
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R.A.Ong
Sep 2005
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The VHE Sky - 2007
>50 sources
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VHE g-ray Science
Origin of
Cosmic
Rays
SNR
s
Gamma-Ray
Bursts
Pulsars
Low E
Microquasars
High E
Testing
Lorentz
Invariance Cold Dark
Matter
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7 Aug 2007 – Berkeley
?
AGN
cosmological
Something g-Ray Horizon
New !
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Major New VHE Telescopes
MAGIC
GLAST (2007)
MILAGRO
VERITAS
(Auger, CR’s)
IceCube, n’s (2011)
HESS
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7 Aug 2007 – Berkeley
CANGAROO
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Cherenkov Telescopes
g-ray
g/hadron separation
g
p
20 km
q ~ 1.5o
1.4 km
Collection area ~ 105 m2
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Cherenkov Telescope Arrays
2
Core
Location
Core Reconstruction (< 15m)
Stereoscopic viewing
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Direction Reconstruction (<0.1o)
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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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7 Aug 2007 – Berkeley
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VERITAS-4 at VERITAS
the Whipple Observatory
F.L. Whipple Basecamp
Mt. Hopkins, AZ (1300m
a.s.l.)
Spring
2007
T4
T1
T3
T2
Since
January
2006
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Fall
2006
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Telescope and Camera
499 PMTs
(Photonis
XP 2970/02)
12m reflector, f1.0 optics
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0.15o pixel
separation,
3.5o FOV
499 pixel Camera
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VERITAS Data Acquisition
Integrated Pulse
48 ns
•
FADC SAMPLES
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7 Aug 2007 – Berkeley
PMTs digitized with 500 MS/s
sampling FADCs
 24 samples/channel/event
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VERITAS Trigger System
3-telescope array
Level One: Pixel
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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7 Aug 2007 – Berkeley
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Supernova Remnants
Pulsar Wind Nebula/Plerion
Supernova Remant (Shell)
• And composites…
• Probable source of cosmic rays up to the “knee”
(~1015 eV)
• Morphology, multi-wavelength…acceleration sites
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7 Aug 2007 – Berkeley
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Old Friends
Mrk421
Mrk501
Crab
Calibration
source
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Pulsar Nebula
AGN
SNR
Other, UNID
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R.A.Ong
Sep 2005
Page 17
VERITAS Performance
angular resolution
•angular resolution on event-byevent basis better than 0.14o
(energy dependent)
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7 Aug 2007 – Berkeley
off-axis sensitivity
•off-axis sensitivity >50% for source
offsets < 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: Γ=-2.55±0.03,
F(E>1 TeV)=(3.1±0.06)x10-7 m-2s-1
•significance ~30 σ/√hour for
three telescope array (7 γ/min)
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7 Aug 2007 – Berkeley
•3 telescope array: Γ=-2.43±0.05,
F(E>1 TeV)=(3.1±0.16)x10-7 m-2s-1
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Figures from Torres et al. Phys. Rep. 382, 303 (2003)
MAGIC point from Albert et al. astro-ph/0705.3119v1
Detection of Supernova Remnant IC 443
EGRET source (overlaps remnant)
IC 443
MAGIC
+
Black – optical
White – EGRET
Color - CO
MAGIC source (first detection in VHE)
overlaps cloud (target material)
•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
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7 Aug 2007 – Berkeley
Crab
Nebula
•Results consistent with MAGIC 5.7 σ
detection in 29 hrs
•position agrees with interaction
zone of molecular cloud
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LS I +61 303: γ-rays from a binary
HMXB: Be-type star coupled with Neutron
Star
Orbital parameters:
• VERITAS observation:
Periastron
(phase 0.23)
Be
star
significance
significance
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orbital period:
~26.5 days
~0.5 AU
•total detection significance: 8.8 σ
(confirms MAGIC discovery)
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Inferior/superior
conjunction
(phase 0.16/0.26))
moonlight
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to observer
•44 h of 2 and 3 telescope data during
5 orbital cycles covering phases 0.30.95
Apastron
(phase 0.73)
LS I +61 303 continued
contemporaneous TeV and X-ray data
orbital phase 0.5-0.8
October 2006
Flux in relative units
energy spectrum
1.2
RXTE 2-10 keV
1.0
VERITAS
0.8
0.6
0.4
0.2
0.
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Orbital phase
• contemporaneous RXTE and Swift
observations over 2 orbital cycles
• power law Γ = -2.6
•maximum flux corresponds to
about 10% of the flux of the Crab
Nebula
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7 Aug 2007 – Berkeley
•correlation between TeV and X-ray
data (both SWIFT and RXTE)
•Sharper peak in gamma-rays
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AGN Detections
• Active Galactic Nuclei
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High-luminosity
extragalactic objects

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Probe properties of
the universe at large
distances
Variable
• AGN observed in VHE
g-rays are
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Mostly blazars
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7 Aug 2007 – Berkeley
Jets aligned with line
of sight
Nearby: z < 0.19
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More old friends: Mrk421 & Mrk501
2 telescope data
• Mrk421
• Mrk501
•~17 hours of observations (April 2006, 2
telescopes)
• 35σ detection
• Active phase
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7 Aug 2007 – Berkeley
•~18.5 hours (April and June 2006, 2
telescopes)
• Low state (not detectible by previous
instruments)
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VERITAS: 1ES 1218+304
• Third furthest VHE blazar (z=0.182)
Raw rates (no zenith angle correction)
• 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
constant flux fit:
χ2=11.21/11
January 2007
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February 2007
March 2007
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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

VLA Image 20cm
• only extragalactic non-blazar
object seen in VHE γ-rays
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Chandra X-ray
VLA Radio
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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)

HST Optical
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VERITAS: M87
•Observation
•44 h with 3-telescope array
• No statistically significant
variability
•5.1 σ, Rate of ~0.1 γ/min
•~1.7% of Crab Nebula flux (E>250
GeV)
θ2-distribution
Flux (% of the Crab Nebula)
light curve
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θ2 [deg2]
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12
10
8
constant flux fit:
χ2=21.4/22
6
4
2
0
February 2007
March 2007
April 2007
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Key Science Projects
SKY SURVEY
SNRs/PWN
BLAZARS
VERITAS
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7 Aug 2007 – Berkeley
DARK MATTER
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VERITAS Sky Survey
2007
2008
• 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)
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Dark Matter KSP
• Indirect detection of dark
matter (e.g. SUSY neutralino
annihilation)
• Dwarf galaxies
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
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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)
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7 Aug 2007 – Berkeley
Limits are more
speculative, but better
chance of detection
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Summary
• VERITAS is now operational!
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Sensitivity of 10% of Crab Nebula flux in < 1hr
Broad scientific program
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Early observations (construction/comissioning phase)
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Sky Survey
SNRs/PWN
Blazars
Dark Matter
Many others..
Several interesting detections
Refinements/optimizations to come
We are looking forward to next season
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7 Aug 2007 – Berkeley
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EXTRA/
BACKUP
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7 Aug 2007 – Berkeley
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VERITAS Trigger System
Level One
CFD x 499
(1 per pixel)
Level Two
Pattern Trigger
Level Delay
Three
Shower
( 1 PDM channel
per trigger signal)
Real-time Array Trigger
(x4 : 1 per telescope)
Array Trigger Coincidence Logic
(SAT Board)
FADC Modules
(1 channel per pixel)
64μs circular buffer
Readout
instructions
Event Logic
Inhibitor
Event
Decision
L3 Trigger
Event
Information
FIFO Buffer
Serialized Event Information
Compensating Delay
( 1 PDM channel
per trigger signal)
Telescope Data
Acquisition System
Harvester Process
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3-telescope array
Trigger System Performance
Array
Single-telescope
Another advantage of stereo!
Dependence of the array trigger
(L3) and pattern trigger rates (L2)
on CFD (L1) thresholds
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7 Aug 2007 – Berkeley
Array dead time α array rate
(typical array rate: 220Hz,
dead time ~10%)
Dominated by data acquisition
→ Partial moonlight capability
(still under study)
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The difference of stereo
- early VERITAS data
p
muon
peak
Single telescope
trigger threshold ~150GeV
Single telescope
analysis threshold ~400GeV
muon ring
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Reconstruction of γ-ray direction
Typical Gamma-ray event
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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
•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, ..
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VERITAS Science Program
• Key Science Projects:

Four highlight science topics.
Discretionary
Bulk Program
10%
40%
• Bulk Science Program


All possible topics.
Determined by TAC selection.
• Discretionary Time


ToO’s, unique topics, engineering.
Determined by Spokesperson.
Key Science Projects
50%
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Sky Survey Observation Scheme
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