Analyzing the December 2013 Orphan Gamma-Ray Flare From 3C 279

TL;DR

This paper models the December 2013 orphan gamma-ray flare from blazar 3C 279 using a leptonic one-zone model with Fermi acceleration, explaining the flare without magnetic reconnection and highlighting shock and stochastic acceleration roles.

Contribution

It introduces a simplified analytic electron energy distribution and demonstrates that Fermi acceleration alone can explain the flare's unique spectral features.

Findings

Fermi acceleration explains the flare without magnetic reconnection.

Shock and stochastic acceleration increase particle energies during the flare.

Outer jet regions show increased external Compton emission.

Abstract

Multiwavelength monitoring of the blazar 3C 279 observed a very bright, 12-hour, orphan gamma-ray flare on 20 Dec 2013 with a uniquely hard Fermi-LAT spectrum and high Compton dominance. We work with a one-zone, leptonic model with both first- and second-order Fermi acceleration, which now reproduces the unique flaring behavior. We present a simplified analytic electron energy distribution to provide intuition about how particle acceleration shapes multi-wavelength blazar jet emission spectra. The contributions of individual processes in relativistic jets is fundamental to understanding the particle energy budget in the formation and propagation of astrophysical jets. We show that first- and second-order Fermi acceleration are sufficient to explain the flare, and that magnetic reconnection is not needed. Our analysis suggests that the flare is initiated by an increase in the particle energies due to shock acceleration, which also increases the stochastic acceleration. The higher energy particle preferentially occupy the outer jet, along the sheath, which decreases the apparent magnetic field and synchrotron radiation, while increasing electron exposure to the broad line region photon fields, driving up the external Compton emission.