HAWC Gus Sinnis VHE Workshop UCLA October, 2005 HAWC: A Next Generation Wide-Field VHE Gamma-Ray Telescope

Gus SinnisVHE Workshop UCLA October, 2005

HAWC

HAWC: A Next Generation Wide-Field VHE Gamma-Ray Telescope


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


HAWC

Effect of Altitude

Approximation B

Low Energy Threshold Requires High Altitude


HAWC

EAS Particle Content – Why Water?

NgammasNelectrons

Primary Energy (GeV)

Low Energy Threshold Requires Detection of Gamma Rays in EAS


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


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


HAWC

HAWC EventsG

amm

asP

roto

ns70 GeV 190 GeV 3 TeV

80 GeV 240 GeV 4 TeV


HAWC

Angular Reconstruction

Same algorithm as Milagro– Core locator– Curvature correction– Sampling correction

(could improve)


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


HAWC

Effective Area – rays

Trigger (nTop>40)Fit < 0.7o

Fit < 0.7o & C>7.0

Squ

are

Met

ers


HAWC

Effective Area: Protons

Protons Trigger/CutGamma Trigger/Cut


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


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


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


HAWC

Point Source Sensitivity


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


HAWC

Simulated Sky Maps

HAWC


HAWC

Survey Sensitivity


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


HAWC

Gamma-Ray Bursts


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


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


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

Documents

HAWC Gus Sinnis VHE Workshop UCLA October, 2005 HAWC: A Next Generation Wide-Field VHE Gamma-Ray Telescope