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

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

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

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

  2. 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 Sinnis VHE Workshop UCLA October, 2005

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

  4. EAS Particle Content – Why Water? Ngammas Nelectrons Primary Energy (GeV) Low Energy Threshold Requires Detection of Gamma Rays in EAS Gus Sinnis VHE Workshop UCLA October, 2005

  5. 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 Sinnis VHE Workshop UCLA October, 2005

  6. e  2 meters 4 meters 300 meters 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 5s in <30 minutes) • ~$30M?? Gus Sinnis VHE Workshop UCLA October, 2005

  7. 70 GeV 190 GeV 3 TeV 4 TeV 80 GeV 240 GeV HAWC Events Gammas Protons Gus Sinnis VHE Workshop UCLA October, 2005

  8. Angular Reconstruction • Same algorithm as Milagro • Core locator • Curvature correction • Sampling correction • sq ~ 0.4o (could improve) Gus Sinnis VHE Workshop UCLA October, 2005

  9. 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 Sinnis VHE Workshop UCLA October, 2005

  10. Effective Area – g rays Trigger (nTop>40) Fit < 0.7o Fit < 0.7o & C>7.0 Square Meters Gus Sinnis VHE Workshop UCLA October, 2005

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

  12. Energy Response – g 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 g/h discrimination does not affect energy response Gus Sinnis VHE Workshop UCLA October, 2005

  13. 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 Sinnis VHE Workshop UCLA October, 2005

  14. HAWC Sensitivity • Again use Monte Carlo and scale from Milagro • Milagro g MC predicts 11 evts/transit (=measured value) for • F=2.68x10-7 E-2.59 m-2 s-1 (Crab declination) • HAWC g 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 g/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) Gus Sinnis VHE Workshop UCLA October, 2005

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

  16. 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 Gus Sinnis VHE Workshop UCLA October, 2005

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

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

  19. 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 Gus Sinnis VHE Workshop UCLA October, 2005

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

  21. 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 Sinnis VHE Workshop UCLA October, 2005

  22. 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 Sinnis VHE Workshop UCLA October, 2005

  23. 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 Gus Sinnis VHE Workshop UCLA October, 2005

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