Observation of the giant radio galaxy M87 with the HEGRA Cherenkov telescopes

Abstract

The giant radio galaxy M87, well studied from radio to X-ray energies, is located in the Virgo cluster of galaxies at a distance of ∼16 Mpc (redshift z=0.00436). M87 has been observed with the HEGRA stereoscopic system of five Cherenkov telescopes in the years 1998 and 1999 for more than 80 h. An excess of TeV γ-rays on the 4 σ level has been found in the data corresponding to an integral flux ( E>730 GeV) of 3.3% of the Crab nebula flux. The HEGRA detection – if confirmed – would make M87 the first TeV γ-ray emitting AGN observed with the imaging atmospheric Cherenkov technique not belonging to the BL Lac class.