The Most Intensive Gamma-Ray Flare of Quasar 3C 279 with the Second-Order Fermi Acceleration

TL;DR

This paper models a rapid gamma-ray flare of quasar 3C 279 using stochastic second-order Fermi acceleration, successfully reproducing observed spectral and temporal features by adjusting magnetic fields.

Contribution

It introduces a time-dependent simulation of turbulent electron acceleration that explains the flare's spectral hardness and light curve asymmetry with minimal parameter changes.

Findings

Hard photon spectrum achieved by decreasing magnetic field.

Rapid cooling explains the light curve decay.

Magnetic energy density is much lower than particle and photon energy densities.

Abstract

The very short and bright flare of 3C 279 detected with {\it Fermi}-LAT in 2013 December is tested by a model with stochastic electron acceleration by turbulences. Our time-dependent simulation shows that the very hard spectrum and asymmetric light curve are successfully reproduced by changing only the magnetic field from the value in the steady period. The maximum energy of electrons drastically grows with the decrease of the magnetic field, which yields a hard photon spectrum as observed. Rapid cooling due to the inverse-Compton scattering with the external photons reproduces the decaying feature of the light curve. The inferred energy density of the magnetic field is much less than the electron and photon energy densities. The low magnetic field and short variability timescale are unfavorable for the jet acceleration model from the gradual Poynting flux dissipation.