Particle Acceleration And Emission Processes In Mrk 421

TL;DR

This paper models the X-ray and gamma-ray flares of Mrk 421 using a two-component SSC approach, revealing different electron acceleration mechanisms and near-equipartition energy densities in the jet regions.

Contribution

It introduces a combined steady and variable component model with distinct acceleration processes to explain multi-band flares in Mrk 421.

Findings

Correlation between X-ray and gamma-ray bands observed.

Flares caused by electron spectrum hardening due to stochastic acceleration.

Electron and magnetic field energy densities are near equipartition.

Abstract

We investigate the X-ray and $\gamma$-ray flares of Mrk 421 on 2008 June 6-15 using the synchrotron self- Compton(SSC) model with electron acceleration, in which an evident correlation between the X-ray and $\gamma$-ray bands appears, while no significant correlation between the optical and X-ray band is observed. We argue that the emission from Mrk 421 may originate from two different components. One is the steady component from the outer region that is mainly attributed to the optical band, in which the electrons are accelerated by first-order Fermi acceleration mechanism. We use a steady electron spectrum to produce the synchrotron self-Compton emission. The other is the variable component from the inner region, in which the electrons are accelerated by the stochastic acceleration process. We use the time-dependent SSC model to produce the emission from the variable component. We suggest that the flares are due to the hardening of the electron spectrum under the process of the stochastic acceleration, which leads to the hardening of the observed spectrum in the X-ray and $\gamma$-ray bands. Furthermore, we find that the energy densities of electrons and magnetic fields are near equipartition in both jet regions.