Letter to the Editor

Probing the cosmic ray population of the giant elliptical galaxy M 87 with observed TeV γ-rays

Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str.1, Postfach 1317, 85741 Garching, Germany

Corresponding author: C. Pfrommer, pfrommer@mpa-garching.mpg.de

Received: 27 May 2003
Accepted: 15 July 2003

Abstract

We examine the cosmic ray proton (CRp) population within the giant elliptical galaxy M 87 using the TeV γ-ray detection of the HEGRA collaboration. In our scenario, the γ-rays are produced by decaying pions which result from hadronic CRp interactions with thermal gas of the interstellar medium of M 87. By comparing the γ-ray emission to upper limits from EGRET, we constrain the spectral index of the CRp population to within our scenario. Both the expected radial γ-ray profile and the required amount of CRp support this hadronic scenario. The accompanying radio mini-halo of hadronically originating cosmic ray electrons is outshone by the synchrotron emission of the relativistic jet of M 87 by one order of magnitude. According to our predictions, the future GLAST mission should allow us to test this hadronic scenario.