Probing the cosmic-ray content of galaxy clusters by stacking Fermi-LAT count maps B. Huber, C. Tchernin, D. Eckert, C. Farnier, A. Manalaysay, U. Straumann and R. Walter A&A, 560 (2013) A64 Published online: 06 December 2013 DOI: 10.1051/0004-6361/201321947