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

TL;DR

This paper analyzes a 2013 gamma-ray flare from blazar 3C 279, revealing uncorrelated multi-wavelength variability and proposing complex multi-zone models to explain the emission mechanisms involved.

Contribution

It introduces two independent modeling approaches—lepto-hadronic and two-zone leptonic—to explain the complex spectral energy distribution during the flare.

Findings

Uncorrelated variability patterns across wavelengths.

Both electron and proton synchrotron processes contribute to emission.

Multiple radiative processes dominate at different times.

Abstract

The blazar 3C 279 exhibited twin $\gamma$-ray flares of similar intensity in 2013 December and 2014 April. In this work, we present a detailed multi-wavelength analysis of the 2013 December flaring event. Multi-frequency observations reveal the uncorrelated variability patterns with X-ray and optical-UV fluxes peaking after the $\gamma$-ray maximum. The broadband spectral energy distribution (SED) at the peak of the $\gamma$-ray activity shows a rising $\gamma$-ray spectrum but a declining optical-UV flux. 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 field 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 $\gamma$-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 flare. In the two-zone modeling, we assume a large emission region emitting primarily in IR to X-rays and $\gamma$-rays to come primarily from a fast moving compact emission region. We conclude by noting that within a span of 4 months, 3C 279 has shown the dominance of a variety of radiative processes over each other and this reflects the complexity involved in understanding the physical properties of blazar jets in general.