MULTI-WAVELENGTH OBSERVATIONS OF 3C 279 DURING THE EXTREMELY BRIGHT GAMMA-RAY FLARE IN 2014 MARCH-APRIL

The well-studied blazar 3C 279 underwent a giant gamma-ray outburst in 2014 March-April. The measured gamma-ray flux (1.21 +/- 0.10 x 10(-5) ph cm(-2) s(-1) in a 0.1-300 GeV energy range) is the highest detected from 3C 279 by the. Fermi Large Area Telescope. Hour-scale gamma-ray flux variability is observed, with a flux doubling time as short as 1.19 +/- 0.36 hr detected during one flare. The gamma-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 gamma-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 gamma-rays. During the flare, a considerable amount of the kinetic jet power gets converted to gamma-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 gamma-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 gamma-ray spectrum.