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The future of ground-based gamma ray astronomy

The future of ground-based gamma ray astronomy. Where do we go?. Outline. … … …. Panic !. Where do we stand ? And how did we get here?. Whipple 1968. H.E.S.S. 2003. Horan & Weeks 2003. Experimental sensitivity in Crab Units. late 1980’s. Theory prediction (SN 1006)

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The future of ground-based gamma ray astronomy

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  1. The future of ground-based gamma ray astronomy Where do we go?

  2. Outline • … • … • …

  3. Panic !

  4. Where do we stand ?And how did we get here?

  5. Whipple1968

  6. H.E.S.S.2003

  7. Horan & Weeks 2003

  8. Experimental sensitivity in Crab Units late 1980’s Theory prediction (SN 1006) “Heinz Völk Units” Inefficient injection late 1990’s High B, low density mid-2000’s 1 0.1 0.01 0.001

  9. 10-6 100 106 1012 Flux sensitivity Peak detected flux / Detection threshold Optical 100000000 Radio 1000000 X-Ray IR 10000 UV Gamma 100 1 Energy [eV] Neutrinos (?)

  10. Is there a future of ground-based gamma ray astronomy ? • Physics issues • Instruments to address these issues

  11. Wish list Sensitivity ~ E-0.8 Aeff1/2hbg-1/2 dq-1

  12. Sensitivity:a no-brainer Horan & Weeks 2003

  13. Angular resolution: Crab viewed with EGRET Crab viewed with HEGRA-CT

  14. Typical TeV beam size Chandra SN 1006 J. Hiraga ASCA/Chandra Angular resolution:Source structure

  15. Wide energy coverage:Acceleration mechanism

  16. Cosmology and structure of space-time Blanch & Martinez 2004 Different EBL models Interaction with extragalactic background light (EBL) Simulated measurements Wide energy coverage:Gamma ray horizon, IR & cosmology AGNs

  17. Large solid angle coverage • Surveys: New sources not visible in other wavelengths • Monitoring of bursts and transients (AGN, GRB, mQuasars,…) HEGRA unidentified Cygnus source

  18. Whipple Mkn 421 Large effective area / rate:MWL correlation of flux and index in AGNs

  19. Need a smart new idea! If I had one, I wouldn’t tell you … from now on: brute force approach …

  20. will concentrate on future beyond current generationA biased view!

  21. Sensitivity, angular resolution:seems hard to beat Cherenkov telescopes • I believe that Cherenkov telescopes are good for at another Generation beyond CANGAROO / H.E.S.S. / MAGIC / VERITAS • Should know: where are the fundamental limits of the technique?

  22. Ultimate limit: use all photons Fit to distribution r(x,y,qx,qy,t) here: using crude representation of distr. function, can probably do better

  23. with geomag. field in bending plane Shower fluctuations:angular resolution: fit to all photons 0.008O/√ETeV

  24. photon statistics shower fluctuations How many photons are needed? 1 GeV 10 GeV 100 GeV 1 TeV relative to PMT quantum efficiency

  25. sy [m] sy [m] 2 TeV p 200 GeV p 1 TeV g 100 GeV g sy [m] sx [m] sx [m] Rejection: ~ 10-2 Shower fluctuations:background rejection Rejection: few 10-4

  26. Conclude: • With enough light (few 10 p.e./GeV), should be able to gain factor ~3 from angular resolution • Similar factor from background rejection (p) • Larger telescopes • (Dense) telescope arrays for low energies • Small pixels  advanced photon detectors • High altitude • Bonus at low energy: geomagnetic cutoff

  27. Optimum telescope size Fixed costs dominate (Control, camera) Dish cost dominates Cost per area 10 m 20 m 30 m Dish size > shower size, depth of field problem ? Triggering on low-energy showers becomes very complex

  28. Focus & depth of field Example: Cherenkov images in a 20 m telescope Focus at infinity Focus on shower head Practical limit around 30 m diameter ? Telescope size = shower width Focus on shower tail Optimum focus

  29. Effect of geomagnetic cutoff A. Plyasheshnikov Practical thresholds A. Plyasheshnikov 30 m telescope @ 5 km @ 1.8 km

  30. Super CANGAROO (M. Mori) Large Telescopes Technical design complete see also: ECO 1000

  31. Thinned CCD GaAs NIM A518, 615 PMT Improved photon detectors Russian groups, MPI Munich/Semicond. Lab Self-quenching Geiger-mode avalanche cells PMT GaAs CCD Signal: 1 : 2.2 : 4.5 S/√B: 1 : 1.1 : 1.4

  32. ALMA site ? A. Konopelko 10 GeV Gamma 5 km 2 km

  33. VHE physicists dream ? • High-resolution mode • Survey / monitoring mode • Large-area mode • Halo of nano-telescopes for 10+ TeV Courtesy NRAO/AUI and ESO

  34. Survey instruments • Cherenkov telescopes with large cameras and Gascoigne aspheric corrector plate … could imagine 10o to 15o diameter • Fresnel lens wide-angle instruments • nontrivial Fresnel lens • huge focal plane (105+ channels) • would probably want several (stereo) instruments of 10 m class

  35. HAWC: A Next Generation All-Sky VHE Gamma-Ray Telescope from G. Sinnis

  36. Angular resolution ~1o Sensitivity 50 mCrab / y for steady sources, ~ 10 h for 1-Crab flare (H.E.S.S.: 30 sec) Median Energy 180 GeV (Milagro ~3 TeV)

  37. Conclusions • Try to get (at least) one Cherenkov telescope system with sub-mCrab sensitivity @ 100 GeV to TeV energies, O(10 GeV) threshold and one wide-angle 100 GeV survey instrument • Unite community • Develop low-cost, no-frills production techniques • Honeycomb foil mirrors a la Durham ? • ASIC for signal storage, trigger, digitisation • …

  38. no magnetic field (< few 10 nT) • atmospheric depth adjustable from 2 r.l. up • combine perfect angular resolution (no low-energy stragglers) with large detection area

  39. Gamma- ray Veto (Drift chamber) Particle shower ~ 10 km ~ 1o Cherenkov light ~ 120 m

  40. replaces geostationary communication satellites

  41. Summary I’m afraid I have nothing really substantial to say … but nevertheless it is hard to fit within less than ½ hour !

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