hawc gus sinnis vhe workshop ucla october, 2005 hawc: a next generation wide-field vhe gamma-ray...
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Gus SinnisVHE Workshop UCLA October, 2005
HAWC
HAWC: A Next Generation Wide-Field VHE Gamma-Ray Telescope
Gus SinnisVHE Workshop UCLA October, 2005
HAWC
Why A Wide-Field Telescope?
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
Gamma Ray Bursts– Prompt Emission– Detect many GRBs for VHE/MeV correlation studies
Extended sources– Diffuse emission from the Galactic plane
• cosmic ray generation and propagation– Molecular clouds– Supernova remnants– Galaxy clusters– Cosmic-ray anisotropy – time variability
Discovery potential Sensitivity is the key element – Goal instantaneous sensitivity of Whipple
Gus SinnisVHE Workshop UCLA October, 2005
HAWC
Effect of Altitude
Approximation B
Low Energy Threshold Requires High Altitude
Gus SinnisVHE Workshop UCLA October, 2005
HAWC
EAS Particle Content – Why Water?
NgammasNelectrons
Primary Energy (GeV)
Low Energy Threshold Requires Detection of Gamma Rays in EAS
Gus SinnisVHE Workshop UCLA October, 2005
HAWC
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
Gus SinnisVHE Workshop UCLA October, 2005
HAWC
HAWC
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 5 in <30 minutes) ~$30M??
e
300 meters
2 meters
4 meters
Gus SinnisVHE Workshop UCLA October, 2005
HAWC
HAWC EventsG
amm
asP
roto
ns70 GeV 190 GeV 3 TeV
80 GeV 240 GeV 4 TeV
Gus SinnisVHE Workshop UCLA October, 2005
HAWC
Angular Reconstruction
Same algorithm as Milagro– Core locator– Curvature correction– Sampling correction
(could improve)
Gus SinnisVHE Workshop UCLA October, 2005
HAWC
Background Rejection
• Similar to Milagro
• nTop = #PMTs in top layer
• cxPE = PEs in brightest bottom layer PMT beyond 20m from fit core
• Cut at C=nTop/cxPE > 7 retains:
– 83% of gamma rays
– 8% of protons
– Sensitivity improves 3x
Protons
Gammas
Gus SinnisVHE Workshop UCLA October, 2005
HAWC
Effective Area – rays
Trigger (nTop>40)Fit < 0.7o
Fit < 0.7o & C>7.0
Squ
are
Met
ers
Gus SinnisVHE Workshop UCLA October, 2005
HAWC
Effective Area: Protons
Protons Trigger/CutGamma Trigger/Cut
Gus SinnisVHE Workshop UCLA October, 2005
HAWC
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
Gus SinnisVHE Workshop UCLA October, 2005
HAWC
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
Gus SinnisVHE Workshop UCLA October, 2005
HAWC
HAWC Sensitivity Again use Monte Carlo and scale from Milagro Milagro MC predicts 11 evts/transit (=measured value) for
– F=2.68x10-7 E-2.59 m-2 s-1 (Crab declination) HAWC MC predicts
– 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)
Milagro detects 20,000 evts/transit background in a 1.2o radius bin around Crab (before /h cut)
HAWC background is then– 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)
Cuts nSignal nBack Significance<1.2o & C>0.0 5248 6.17 x 105 6transit
<0.7o & C>0.0 3900 2.1 x 105 8transit
<0.7o & C>7.0 3230 (~0.2 Hz) 16,654 25transit
Gus SinnisVHE Workshop UCLA October, 2005
HAWC
Point Source Sensitivity
Gus SinnisVHE Workshop UCLA October, 2005
HAWC
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 in one year
Gus SinnisVHE Workshop UCLA October, 2005
HAWC
Simulated Sky Maps
HAWC
Gus SinnisVHE Workshop UCLA October, 2005
HAWC
Survey Sensitivity
Gus SinnisVHE Workshop UCLA October, 2005
HAWC
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 5 detection for a 100
second observation
Gus SinnisVHE Workshop UCLA October, 2005
HAWC
Gamma-Ray Bursts
Gus SinnisVHE Workshop UCLA October, 2005
HAWC
Work Needed/In Progress Simulation work
– 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
Gus SinnisVHE Workshop UCLA October, 2005
HAWC
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
Gus SinnisVHE Workshop UCLA October, 2005
HAWC
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
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