Letter to the Editor

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

¹ 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

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

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 σ. 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 and is a promising candidate among the class of giant radio galaxies for the emission of TeV γ-radiation. The detection of TeV γ-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.