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MPI Kernphysik, Heidelberg Humboldt Univ. Berlin Ruhr-Univ. Bochum Univ. Hamburg

Ground-Based Gamma Ray Astronomy at Energies > 10 TeV (H.E.S.S. et al. & beyond......) Gavin Rowell (MPIK Heidelberg). MPI Kernphysik, Heidelberg Humboldt Univ. Berlin Ruhr-Univ. Bochum Univ. Hamburg Landessternwarte Heidelberg Univ. Kiel Ecole Polytechnique, Palaiseau

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MPI Kernphysik, Heidelberg Humboldt Univ. Berlin Ruhr-Univ. Bochum Univ. Hamburg

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  1. Ground-Based Gamma Ray Astronomyat Energies > 10 TeV(H.E.S.S. et al. & beyond......)Gavin Rowell (MPIK Heidelberg) MPI Kernphysik, Heidelberg Humboldt Univ. Berlin Ruhr-Univ. Bochum Univ. Hamburg Landessternwarte Heidelberg Univ. Kiel Ecole Polytechnique, Palaiseau College de France, Paris Univ. Paris VI-VII Univ. Montpellier II MPI Kernphysik, Heidelberg Humboldt Univ. Berlin Ruhr-Univ. Bochum Univ. Hamburg Landessternwarte Heidelberg Univ. Kiel Ecole Polytechnique, Palaiseau College de France, Paris Univ. Paris VI-VII Univ. Montpellier II

  2. Lessons from H.E.S.S. data of 2003/2004 - Hard spectra for most new TeV sources. - Most skymaps (of galactic sources) are produced using Hard cuts (Q < 0.1°, image SIZE > 200 pe., >= 2 tels) --> improved CR bkg rejection --> improved angular resolution (high E events trigger >2 tels) - Hard spectra motivates further efforts for E > 10 TeV detection (Astrophysical motivations are clear and discussed this week) Investigate - HESS performance at E > 10 TeV at high zenith angles - New dedicated telescopes for E > 10 TeV astronomy

  3. E < 0.6 TeV 0.6 < E < 1.4 E > 1.4 TeV Morphology of Gamma-Ray Sources eg. the hard spectrum of RXJ1713 permits good statistics well above HESS threshold. Images below have the same gamma excess (overall) RX J1713.7-3946 HESS Preliminary

  4. The Crab Pulsar Wind Nebula Strong, steady source at all wavelengths - Standard candle - Spectrum measured up to ~ 70 TeV (HEGRA) --> Particle accel to E > 100 TeV (GeV sync + IC) Aharonian et al. 2004 (HEGRA) Inverse Compton (various seed photons)

  5. H.E.S.S. Crab: HESS & HEGRA Results HESS ~ 30 hrs data E>250 GeV 7-10 gammas/min ~ 30 sigma/sqrt(hr) ZA>40° --> spectrum consistent with HEGRA dN/dE ~ E -2.6 paper in preparation HEGRA (1997 - 2002) - Over 300 hrs data E > 500 GeV 1-2 gammas/min ~ 10 sigma/sqrt(hr) Aharonian et al. 2004 (HEGRA)

  6. HESS Collection Area: After 'Standard' Cuts (Q < 0.112°, Image SIZE > 80 pe., >= 2 tels) Energy & Zenith Angle Aeff approaches 1 km2 ZA >= 60° Use increasing atm. thickness with ZA: --> EAS/Cerenkov more spread out --> EAS can trigger further away > 1000m ! Sommers & Elbert (1987) Zenith angle (ZA)

  7. HESS Crab: Compare Med/High ZA for E > 10 TeV Use runs with 4 telescopes & Crab <= 1.0° off-axis Q < 0.112° + 'standard' shape cuts, >= 2 tels ZA <= 40° (medium zenith) 4.10.6 gam/hr 7.0 sigma 5.9 hrs 3.2 sigma/sqrt(hr) ZA >= 60° (high zenith) 8.11.6 gam/hr 4.9 sigma 2.2 hrs 3.3 sigma/sqrt(hr) --> High ZA observation definitely viable. Improved evt rate, similar sigma/sqrt(hr)..... Improved angular res for High ZA expected --> even better! --> Crab has a rather steep spectrum: Better for hard spectra.

  8. Horns et al. (2004), Aharonian et al. (2005) Night of MJD 53113 CR rate Gam rate dN/dE ~ E-2.1+-0.1 exp(-E/3.1+-0.5) H.E.S.S. Obs. Of Mkn 421 at High ZA - Apr – May 2004 (9 nights, 10 hours) - ZA ~ 61° to 65° - Eth ~ 1.5 TeV - Aeff ~ 2 km2 (> 10 TeV) - <rate> ~ 8 gam/min peak 14 gam/min (4 Crab) - ~7000 gam >100 sigma - flux change factor 4 to 5 internight. - also intranight variability - Good stability of atm. CR rate constant ~ few % (after run selection)

  9. L L A Dedicated Cerenkov Imaging System for E > 10 TeV Astronomy Consider an array of Telescopes (we want stereo!): - Telescope mirror area A - Camera FoV & pixel size - Array size/dimension L Results based on earlier MC simulation study: Plyasheshnikov et al. (2000) J. Phys. G: Nucl. Part. Phys. v. 26, p183 - employed ALTAI shower simulation code 0.7 to 200 TeV gammas, 1.5 to 300 TeV protons --> use these results to suggest the fundamental design.......

  10. Lateral Distribution Cerenkov Image pe. 'Size' vs. Impact Param 'R' Mirror area A x QE = 1 m2 ie. A = 10 m2 QE = 0.1 Infinite FoV camera --> 10 m2 perfectly adequate for E > 10 TeV --> sufficient Cerenkov pe. R > 500m Gamma (solid) Protons (dashed) 100 pe.

  11. FoV Dist Image First Look at Cerenkov Image Centroid 'Dist' vs. Impact Param 'R' Single Telescope Gamma EAS (on-axis) FoV = 9.3° Pixel Trigger q = 15 pe. --> Need large FoV ~ 9° – 10°

  12. Array Dimension & FoV of each Telescope Detection Efficiency vs. FoV (Cell of 4 telescopes) Gamma EAS (on axis) L L L = 333 m L = 500 m --> FoV ~9° – 10° recommended ...esp. for extended srcs!

  13. Array Data Analysis Cerenkov Image Parameters: Hillas (1985) moment approach width, length, major-axes etc + image cleaning (tailcuts) Stereo gamma/hadron separation: Mean-scaled-width (MSW) MSW =  wi / wexpected,i sum over tels Stereo direction reconstruction: Intersecting pairs of image major axes (Hofmann et al. 1999)  ang. res ~0.15° is achieved --> apply MSW + direction cuts (CR bkg rejection) same as for HEGRA, HESS, VERITAS .....

  14. Array Performance (E > 8-10 TeV) Array: 4 telescopes L = 500m, q=10 pe., pixel size 0.3°, FoV = 9.3° Crab-like flux & spectrum (vertical) Ethres ~ 8 - 10 TeV before after direction + shape cuts Rgamma 3.4 1.7 evts/hr Rprotons 702 0.2 --> sig/bkg ~ 9 compare to: HESS ~5 gam/hr sig/bkg ~ 20 (ZA>40deg!) (E > 8 TeV) HEGRA ~2 sig/bkg ~4 • -> A modest 4-tel array ~ HESS performance • (sims used conservative QE, mirror area..)

  15. Summary High Zenith Angle Obs for E>10 TeV: Already verified with HEGRA & HESS! (VERITAS...in future) Aeff >= few km2 Interesting Consequence: High ZA Obs. of Southern sources by VERITAS v. useful! (such sources available 2-4 hrs/night) Vice versa for HESS obs of Northern sources. Dedicated Array of Cerenkov Imaging Telescopes for E>10 TeV Require modest mirror area ~10 m2 Large FoV ~ 9 to 10° Telescope spacing large > 300 m Good sensitivity for a modest 4-tel array - extend to many more telescopes & optimise detector parameters....further work

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