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 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 broadline region (BLR) and contributions from both BLR and torus photons are required to explain the observed γ-ray spectrum.