Jim Hinton MPI-R, Bonn 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 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

Jim Hinton MPI-R, Bonn Lessons from H.E.S.S. data of 2003/ Hard spectra for most new TeV sources. - Most skymaps (of galactic sources) are produced using Hard cuts (  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

Jim Hinton MPI-R, Bonn E 1.4 TeV eg. the hard spectrum of RXJ1713 permits good statistics well above HESS threshold. Images below have the same gamma excess (overall) RX J Morphology of Gamma-Ray Sources HESS Preliminary

Jim Hinton MPI-R, Bonn 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) Inverse Compton (various seed photons) Aharonian et al (HEGRA)

Jim Hinton MPI-R, Bonn 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 ( ) - Over 300 hrs data E > 500 GeV 1-2 gammas/min ~ 10 sigma/sqrt(hr) H.E.S.S. Aharonian et al (HEGRA)

Jim Hinton MPI-R, Bonn HESS Collection Area: After 'Standard' Cuts (  80 pe., >= 2 tels) Energy & Zenith Angle A eff approaches 1 km 2 ZA >= 60° Zenith angle (ZA) Use increasing atm. thickness with ZA: --> EAS/Cerenkov more spread out --> EAS can trigger further away > 1000m ! Sommers & Elbert (1987)

Jim Hinton MPI-R, Bonn HESS Crab: Compare Med/High ZA for E > 10 TeV Use runs with 4 telescopes & Crab <= 1.0° off-axis  = 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.

Jim Hinton MPI-R, Bonn Horns et al. (2004), Aharonian et al. (2005) dN/dE ~ E exp(-E/ ) H.E.S.S. Obs. Of Mkn 421 at High ZA - Apr – May 2004 (9 nights, 10 hours) - ZA ~ 61° to 65° - E th ~ 1.5 TeV - A eff ~ 2 km 2 (> 10 TeV) - ~ 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) Night of MJD CR rate Gam rate

Jim Hinton MPI-R, Bonn 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 L L

Jim Hinton MPI-R, Bonn Lateral Distribution Cerenkov Image pe. 'Size' vs. Impact Param 'R' Mirror area A x QE = 1 m 2 ie. A = 10 m 2 QE = 0.1 Infinite FoV camera --> 10 m 2 perfectly adequate for E > 10 TeV --> sufficient Cerenkov pe. R > 500m 100 pe. Gamma (solid) Protons (dashed)

Jim Hinton MPI-R, Bonn 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. Dist FoV Image --> Need large FoV ~ 9° – 10°

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

Jim Hinton MPI-R, Bonn 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 =  w i / w expected,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.....

Jim Hinton MPI-R, Bonn 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) E thres ~ TeV before after direction + shape cuts R gamma evts/hr R protons > 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..)

Jim Hinton MPI-R, Bonn Summary High Zenith Angle Obs for E>10 TeV: Already verified with HEGRA & HESS! (VERITAS...in future) Aeff >= few km 2 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 m 2 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