A Hard gamma-ray flare from 3C 279 in 2013 December

Abstract

The blazar 3C 279 exhibited twin γ -ray fl ares of similar intensity in 2013 December and 2014 April. In this work, we present a detailed multi-wavelength analysis of the 2013 December fl aring event. Multi-frequency observations reveal the uncorrelated variability patterns with X-ray and optical – UV fl uxes peaking after the γ -ray maximum. The broadband spectral energy distribution ( SED ) at the peak of the γ -ray activity shows a rising γ -ray spectrum but a declining optical – UV fl ux. This observation along with the detection of uncorrelated variability behavior rules out the one-zone leptonic emission scenario. We, therefore, adopt two independent methodologies to explain the SED: a time-dependent lepto-hadronic modeling and a two-zone leptonic radiative modeling approach. In the lepto-hadronic modeling, a distribution of electrons and protons subjected to a randomly orientated magnetic fi eld produces synchrotron radiation. Electron synchrotron is used to explain the IR to UV emission while proton synchrotron emission is used to explain the high-energy γ -ray emission. A combination of both electron synchrotron self-Compton emission and proton synchrotron emission is used to explain the X-ray spectral break seen during the later stage of the fl are. In the two-zone modeling, we assume a large emission region emitting primarily in IR to X-rays and γ -rays to come primarily from a fast-moving compact emission region. We conclude by noting that within a span of four months, 3C 279 has shown the dominance of a variety of radiative processes over each other and this re fl ects the complexity involved in understanding the physical properties of blazar jets in general.