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

2. HAWC Gus Sinnis VHE Workshop UCLA October, 2005 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

3. HAWC Gus Sinnis VHE Workshop UCLA October, 2005 Effect of Altitude Approximation B Low Energy Threshold Requires High Altitude

4. 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

5. HAWC Gus Sinnis VHE Workshop UCLA October, 2005 Milagro – Lessons Learned  Optical isolation of PMTs is critical –Cherenkov angle 41 o 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

6. HAWC Gus Sinnis VHE Workshop UCLA October, 2005 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

7. HAWC Gus Sinnis VHE Workshop UCLA October, 2005 HAWC Events 30 GeV70 GeV230 GeV 20 GeV70 GeV 270 GeV Gammas Protons

8. HAWC Gus Sinnis VHE Workshop UCLA October, 2005 HAWC Events Gammas Protons 70 GeV190 GeV3 TeV 80 GeV240 GeV 4 TeV

9. HAWC Gus Sinnis VHE Workshop UCLA October, 2005 Angular Reconstruction  Same algorithm as Milagro –Core locator –Curvature correction –Sampling correction      (could improve)

10. 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 Cut at C=nTop/cxPE > 7 retains: – 83% of gamma rays – 8% of protons – Sensitivity improves 3x Protons Gammas

11. HAWC Gus Sinnis VHE Workshop UCLA October, 2005 Effective Area –  rays Trigger (nTop>40) Fit < 0.7 o Fit 7.0 Square Meters

12. HAWC Gus Sinnis VHE Workshop UCLA October, 2005 Effective Area: Protons Protons Trigger/Cut Gamma Trigger/Cut

13. HAWC Gus Sinnis VHE Workshop UCLA October, 2005 Energy Response –  rays Crab Spectrum 2.62x10 -7 E -2.59 Events that fit within 0.7 o of true direction and C>7.0 Median 250 GeV  /h discrimination does not affect energy response

14. 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

15. HAWC Gus Sinnis VHE Workshop UCLA October, 2005 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 ( 0.0) –3900 evts/transit ( 0.0) –3230 evts/transit ( 7.0)  Milagro detects 20,000 evts/transit background in a 1.2 o radius bin around Crab (before  /h cut)  HAWC background is then –617,000 evts/transit ( 0.0) –210,000 evts/transit ( 0.0) –16,654 evts/transit ( 7.0) CutsnSignalnBackSignificance 0.0 52486.17 x 10 5 6  transit 0.0 39002.1 x 10 5 8  transit 7.0 3230 (~0.2 Hz)16,654 25  transit

16. HAWC Gus Sinnis VHE Workshop UCLA October, 2005 Point Source Sensitivity

17. HAWC Gus Sinnis VHE Workshop UCLA October, 2005 Simulated Sky Maps  Background map (0.1 o x 0.1 o 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 (0.7 o radius – used square bin of equal area) –Compare signal and background  HAWC sees 26/35 at > 5  in one year

18. HAWC Gus Sinnis VHE Workshop UCLA October, 2005 Simulated Sky Maps HAWC

19. Gus Sinnis VHE Workshop UCLA October, 2005 Survey Sensitivity

20. 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 5  detection for a 100 second observation

21. HAWC Gus Sinnis VHE Workshop UCLA October, 2005 Gamma-Ray Bursts

22. HAWC Gus Sinnis VHE Workshop UCLA October, 2005 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

23. 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

24. 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  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