Electron Acceleration In Blazars: Application to the 3C 279 Flare on 2013 December 20

TL;DR

This paper models the 2013 December 20 gamma-ray flare of blazar 3C 279 using a one-zone jet model, explaining the spectral energy distribution with Fermi acceleration processes without invoking magnetic reconnection.

Contribution

It introduces a comprehensive one-zone blazar jet model that reproduces both quiescent and flaring states, including an analytic approximation for electron distribution.

Findings

Fermi acceleration explains the flare without magnetic reconnection.

The model reproduces the unusual SED with hard gamma-ray spectrum.

Insufficient energy for a simultaneous X-ray flare was identified.

Abstract

The broadband spectrum from the 2013 December 20 $\gamma$-ray flare from 3C~279 is analyzed with our previously-developed one-zone blazar jet model. We are able to reproduce two SEDs, a quiescent and flaring state, the latter of which had an unusual SED, with hard $\gamma$-ray spectrum, high Compton dominance, and short duration. Our model suggests that there is insufficient energy for a comparable X-ray flare to have occurred simultaneously, which is an important constraint given the lack of X-ray data. We show that first- and second-order Fermi acceleration are sufficient to explain the flare, and that magnetic reconnection is not needed. The model includes particle acceleration, escape, and adiabatic and radiative energy losses, including the full Compton cross-section, and emission from the synchrotron, synchrotron self-Compton, and external Compton processes. We provide a simple analytic approximation to the electron distribution solution to the transport equation that may be useful for simplified modeling in the future.