A&A 403, L1-L5 (2003)
DOI: 10.1051/0004-6361:20030372

Letter

Is the giant radio galaxy M 87 a TeV gamma-ray emitter?

F. Aharonian¹, A. Akhperjanian², M. Beilicke³, K. Bernlöhr¹, H.-G. Börst⁴, H. Bojahr⁵, O. Bolz¹, T. Coarasa⁶, J. L. Contreras⁷, J. Cortina⁸, S. Denninghoff⁶, M. V. Fonseca⁷, M. Girma¹, N. Götting³, G. Heinzelmann³, G. Hermann¹, A. Heusler¹, W. Hofmann¹, D. Horns¹, I. Jung¹, R. Kankanyan¹, M. Kestel⁶, A. Kohnle¹, A. Konopelko¹, H. Kornmeyer⁶, D. Kranich⁶, H. Lampeitl³, M. Lopez⁷, E. Lorenz⁶, F. Lucarelli⁷, O. Mang⁴, H. Meyer⁵, R. Mirzoyan⁶, A. Moralejo⁷, E. Ona-Wilhelmi⁷, M. Panter¹, A. Plyasheshnikov^{1, 9}, G. Pühlhofer¹, R. de los Reyes⁷, W. Rhode⁵, J. Ripken³, G. Rowell¹, V. Sahakian², M. Samorski⁴, M. Schilling⁴, M. Siems⁴, D. Sobzynska^{6, 10}, W. Stamm⁴, M. Tluczykont³, V. Vitale⁶, H. J. Völk¹, C. A. Wiedner¹ and W. Wittek<sup>6

1</sup>  Max-Planck-Institut für Kernphysik, Postfach 103980, 69029 Heidelberg, Germany
²  Yerevan Physics Institute, Alikhanian Br. 2, 375036 Yerevan, Armenia
³  Universität Hamburg, Institut für Experimentalphysik, Luruper Chaussee 149, 22761 Hamburg, Germany
⁴  Universität Kiel, Institut für Experimentelle und Angewandte Physik, Leibnizstraße 15-19, 24118 Kiel, Germany
⁵  Universität Wuppertal, Fachbereich Physik, Gaußstr.20, 42097 Wuppertal, Germany
⁶  Max-Planck-Institut für Physik, Föhringer Ring 6, 80805 München, Germany
⁷  Universidad Complutense, Facultad de Ciencias Físicas, Ciudad Universitaria, 28040 Madrid, Spain
⁸  Now at Institut de Física d'Altes Energies, UAB, Edifici Cn, 08193, Bellaterra (Barcelona), Spain
⁹  On leave from Altai State University, Dimitrov Street 66, 656099 Barnaul, Russia
¹⁰  Home institute: University Lodz, Poland

(Received 10 February 2003 / Accepted 12 March 2003 )

Abstract
For the first time an excess of photons above an energy threshold of 730 GeV from the giant radio galaxy M 87 has been measured at a significance level above 4 . The data have been taken during the years 1998 and 1999 with the HEGRA stereoscopic system of 5 imaging atmospheric Cherenkov telescopes. The excess of  events above 730 GeV corresponds to an integral flux of 3.3% of the Crab flux or  phot cm ^-2 s ^-1. M 87 is located at the center of the Virgo cluster of galaxies at a relatively small redshift of z = 0.00436 and is a promising candidate among the class of giant radio galaxies for the emission of TeV -radiation. The detection of TeV -rays from M 87 - if confirmed - would establish a new class of extragalactic source in this energy regime since all other AGN detected to date at TeV energies are BL Lac type objects.

Key words: -rays: observations -- galaxies: individual: M 87

Offprint request: N. Götting, M. Tluczykont [Niels.Goetting; Martin.Tluczykont]@desy.de

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© ESO 2003

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