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

Abstract We report multiwavelength (infrared–optical, ultraviolet, X-ray and γ-ray) data from 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 on board Fermi of γ-rays with energy above 10 GeV indicates that the emission likely occurs beyond the highly opaque (τ ∼ 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 γ-ray flux. We discuss the possibility that short-term variability results from fast magnetic reconnection events, as proposed in recent works.