Multi-wavelength observations of 3C 279 during the extremely bright gamma-ray flare in 2014 March-April

Abstract

The well-studied blazar 3C 279 underwent a giant γ-ray outburst in 2014 March-April. The measured γ-ray flux (1.21 ± 0.10 × 10-5 in a 0.1-300 GeV energy range) is the highest detected from 3C 279 by the Fermi Large Area Telescope. Hour-scale γ-ray flux variability is observed, with a flux doubling time as short as 1.19 ± 0.36 hr detected during one flare. The γ-ray spectrum is found to be curved at the peak of the flare, suggesting low probability of detecting very high energy (VHE; E 100 GeV) emission, which is further confirmed by the VERITAS observations. The γ-ray flux increased by more than an order in comparison to a low-activity state and the flare consists of multiple sub-structures having a fast rise and slow decay profile. The flux enhancement is seen in all the wavebands, though at a lesser extent compared to γ-rays. During the flare, a considerable amount of the kinetic jet power gets converted to γ-rays and the jet becomes radiatively efficient. A one-zone leptonic emission model is used to reproduce the flare and we find increase in the bulk Lorentz factor as a major cause of the outburst. From the observed fast variability, lack of VHE detection, and the curved γ-ray spectrum, we conclude that the location of the emission region cannot be far out from the broad-line region (BLR) and contributions from both BLR and torus photons are required to explain the observed γ-ray spectrum.