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

TL;DR

This paper reports on the 2014 gamma-ray flare of blazar 3C 279, highlighting its extreme brightness, rapid variability, spectral curvature, and the implications for emission region location and jet physics.

Contribution

It presents multi-wavelength observations of the brightest 3C 279 flare, modeling the emission with a one-zone leptonic model and analyzing the flare's characteristics and origin.

Findings

Highest gamma-ray flux from 3C 279 detected by Fermi.

Rapid flux doubling time of about 1.2 hours during the flare.

Emission region likely close to the broad line region, involving both BLR and torus photons.

Abstract

The well studied blazar 3C 279 underwent a giant $\gamma$-ray outburst in 2014 March-April. The measured $\gamma$-ray flux (1.21 $\pm$ 0.10 $\times$ 10$^{-5}$ ph cm$^{-2}$ s$^{-1}$ in 0.1-300 GeV energy range) is the highest detected from 3C 279 by Fermi Large Area Telescope. Hour scale $\gamma$-ray flux variability are observed, with a flux doubling time as short as 1.19 $\pm$ 0.36 hours detected during one flare. The $\gamma$-ray spectrum is found to be curved at peak of the flare suggesting low probability of detecting very high energy (VHE; E $>$ 100 GeV) emission, which is further confirmed by the Very Energetic Radiation Imaging Telescope Array System observations. The $\gamma$-ray flux increased by more than an order in comparison to low activity state and the flare consists of multiple sub-structures having 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.