The far emission region of the gamma-ray blazar PKS B1424-418

Abstract: We report multi-wavelength (IR-O, UV, X-ray, gamma-ray) data of the flat spectrum radio quasar (FSRQ) PKS B1424-418 (z=1.52) gathered during an active phase in 2013 April . As for a few other cases of FSRQs reported in literature, the detection by the Large Area Telescope onboard Fermi of gamma rays with energy above 10 GeV indicates that the emission likely occurs beyond the highly opaque (tau ~10) broad line region. This conclusion is strengthened by a model fit to the spectral energy distribution, which allows us to locate the emission region even beyond the distance generally assumed for the dusty torus. The consequent large size (~1 pc) inferred for the emission region cannot account for the observed daily-scale variability of the gamma-ray flux. We discuss the possibility that short-term variability results from fast magnetic reconnection events, as proposed in recent works.