Transcript Document

HAWC: A Next Generation Wide-Field VHE
Gamma-Ray Telescope
HAWC
Gus Sinnis
VHE Workshop UCLA October, 2005
Why A Wide-Field Telescope?
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Complete unbiased sky survey
AGN Physics
– Obtain population statistics on flares (power spectra)
– Study long-term behavior of many AGN
– Extend GLAST measurements to higher energies
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Gamma Ray Bursts
– Prompt Emission
– Detect many GRBs for VHE/MeV correlation studies
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Extended sources
– Diffuse emission from the Galactic plane
• cosmic ray generation and propagation
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Molecular clouds
Supernova remnants
Galaxy clusters
Cosmic-ray anisotropy – time variability
Discovery potential
Sensitivity is the key element – Goal instantaneous sensitivity of Whipple
HAWC
Gus Sinnis
VHE Workshop UCLA October, 2005
Effect of Altitude
Approximation B
Low Energy Threshold Requires High Altitude
HAWC
Gus Sinnis
VHE Workshop UCLA October, 2005
EAS Particle Content – Why Water?
Ngammas
Nelectrons
Primary Energy (GeV)
Low Energy Threshold Requires Detection
of Gamma Rays in EAS
HAWC
Gus Sinnis
VHE Workshop UCLA October, 2005
Milagro – Lessons Learned
 Optical isolation of PMTs is critical
– Cherenkov angle 41o and clear water leads to optical cross-talk
of distant PMTs
– Improves angular and energy resolution
– Improves background rejection
 Size matters – large detector enables
– Better angular resolution (longer lever arm)
– Better background rejection (higher probability of intercepting a
muon or hadron)
– Sensitivity ~ Area
 Altitude matters
– Closer to shower max lowers energy threshold
– Tibet altitude has 5x more particles for same shower as Milagro
HAWC
Gus Sinnis
VHE Workshop UCLA October, 2005
HAWC
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2 meters
4 meters
300
meters
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11250 PMTs (5625/layer)
4 meter spacing
2 meter top layer depth
6 meter bottom layer depth
Trigger rate ~80 kHz
Location Tibet (4300m) or Chile (5200m)
>60x Milagro sensitivity (Crab 5s in <30 minutes)
~$30M??
HAWC
Gus Sinnis
VHE Workshop UCLA October, 2005
HAWC Events
190 GeV
3 TeV
Gammas
70 GeV
240 GeV
4 TeV
Protons
80 GeV
HAWC
Gus Sinnis
VHE Workshop UCLA October, 2005
Angular Reconstruction
 Same algorithm as Milagro
– Core locator
– Curvature correction
– Sampling correction
 sq ~ 0.4o (could improve)
HAWC
Gus Sinnis
VHE Workshop UCLA October, 2005
Background Rejection
• Similar to Milagro
• nTop = #PMTs in top layer
• cxPE = PEs in brightest
bottom layer PMT beyond 20m
from fit core
Protons
Gammas
• Cut at C=nTop/cxPE > 7
retains:
– 83% of gamma rays
– 8% of protons
– Sensitivity improves 3x
HAWC
Gus Sinnis
VHE Workshop UCLA October, 2005
Square Meters
Effective Area –  rays
HAWC
Trigger (nTop>40)
Fit < 0.7o
Fit < 0.7o & C>7.0
Gus Sinnis
VHE Workshop UCLA October, 2005
Effective Area: Protons
Protons Trigger/Cut
Gamma Trigger/Cut
HAWC
Gus Sinnis
VHE Workshop UCLA October, 2005
Energy Response –  rays
Crab Spectrum
2.62x10-7 E-2.59
Events that fit within
0.7o of true direction
and C>7.0
Median 250 GeV
/h discrimination
does not affect
energy response
HAWC
Gus Sinnis
VHE Workshop UCLA October, 2005
Background Rate Estimation
 Scale from Milagro rate – more robust
than dead reckoning
 Milagro Monte Carlo protons (arb flux E-2.7)
gives 85 events/transit for Crab declination
 HAWC Monte Carlo gives 2600 evts/trnsit
 Therefore HAWC trigger rate
= 2600/85 = 31 x Milagro(1.7kHz) = 53kHz
HAWC
Gus Sinnis
VHE Workshop UCLA October, 2005
HAWC Sensitivity
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Again use Monte Carlo and scale from Milagro
Milagro  MC predicts 11 evts/transit (=measured value) for
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F=2.68x10-7 E-2.59 m-2 s-1 (Crab declination)
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5248 evts/transit (<1.2o of source & C>0.0)
3900 evts/transit (<0.7o of source & C>0.0)
3230 evts/transit (<0.7o of source & C>7.0)
HAWC  MC predicts
Milagro detects 20,000 evts/transit background in a 1.2o radius bin around Crab
(before /h cut)
HAWC background is then
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Cuts
617,000 evts/transit (<1.2o of source & C>0.0)
210,000 evts/transit (<0.7o of source & C>0.0)
16,654 evts/transit (<0.7o of source & C>7.0)
nSignal
nBack
Significance
<1.2o & C>0.0
5248
6.17 x 105
6s/transit
<0.7o & C>0.0
3900
2.1 x 105
8s/transit
<0.7o & C>7.0
3230 (~0.2 Hz)
16,654
25s/transit
HAWC
Gus Sinnis
VHE Workshop UCLA October, 2005
Point Source Sensitivity
HAWC
Gus Sinnis
VHE Workshop UCLA October, 2005
Simulated Sky Maps
 Background map (0.1o x 0.1o bins) is generated using the observed
Milagro declination distribution of events scaled to the HAWC rate
 Signal map is generated by Poisson fluctuating counts in each bin of
background map then adding signal events
– 6 Known Northern hemisphere sources
• Crab, Mrk501, Mrk421, 1ES1959+60, H1426+428, CYG OB
– 2 Milagro extended sources (Cygnus region, EGRET unID)
– 27 Costamante & Ghisellini AGN (Kneiske et al. IR model)
 Signal is added by spreading events over 10 degree radius around
source according to point-spread function as given by the Monte
Carlo (non-Gaussian)
 Maps are then analyzed just as real data
– Sum signal and background maps over bin size commensurate with
angular resolution (0.7o radius – used square bin of equal area)
– Compare signal and background
 HAWC sees 26/35 at > 5 s in one year
HAWC
Gus Sinnis
VHE Workshop UCLA October, 2005
Simulated Sky Maps
HAWC
HAWC
Gus Sinnis
VHE Workshop UCLA October, 2005
Survey Sensitivity
HAWC
Gus Sinnis
VHE Workshop UCLA October, 2005
Gamma Ray Bursts
 Assume E-2 spectrum from GRB
 Evolve spectrum through IR field
– Use Kneiske et al. IR model
 Calculate effective area for each energy and
zenith angle (gammas and protons)
 For each zenith angle calculate background by
scaling from Milagro
 Determine gamma-ray rate for given flux
 Scale flux to yield a 5s detection for a 100
second observation
HAWC
Gus Sinnis
VHE Workshop UCLA October, 2005
Gamma-Ray Bursts
HAWC
Gus Sinnis
VHE Workshop UCLA October, 2005
Work Needed/In Progress
 Simulation work
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Incorporate muon background into events
Optimize reconstruction algorithms for HAWC
Develop energy reconstruction algorithm
Can a single layer perform as well?
 Test of curtains
– Now in place in Milagro (16 PMTs are “curtained”)
– Singles rates dropped by factor of 2-3 (20 kHz to 7 kHz)
– Study angular resolution (are timing distributions better?)
 Calibration with curtains
– In progress in Milagro
– Better method with HAWC (transparent in red opaque in UV curtains?)
 Test of singles rates vs. altitude
– Portable water tank with daq system built and operated
– Took data at several altitudes (Colorado and New Mexico)
• ~2x increase at 14,000 feet (needs verification) for soft component
HAWC
Gus Sinnis
VHE Workshop UCLA October, 2005
Work Needed/In Progress
 Data acquisition system needs design/build
 Cost estimates for infrastructure
– Pond
– Cover or building
– Water system
 Improved encapsulation scheme
– Failure rate < 1%/year
 PMT recovery system
 People – much bigger project than Milagro
HAWC
Gus Sinnis
VHE Workshop UCLA October, 2005
Conclusions
 An all-sky VHE instrument with Whipple-like
sensitivity can be built for ~$30M
 Can survey sky to <15 mCrab in 1 year
– <5 mCrab after 10 year of operations
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Transients – 2x Crab in <8 minutes
GRB sensitivity to ~1/1000 of ~20keV flux
Discovery potential is great
We would like to be up with GLAST
We need a bigger collaboration
HAWC
Gus Sinnis
VHE Workshop UCLA October, 2005