The awakening of BL Lacertae: observations by Fermi, Swift, and the GASP-WEBT

C. M. Raiteri, M. Villata, F. D'Ammando +4

Since the launch of the Fermi satellite, BL Lacertae has been moderately active at gamma-rays and optical frequencies until May 2011, when the source started a series of strong fla…