Particle Acceleration and Emission Processes in Mrk 421

Abstract

We investigated the X-ray and γ-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 γ-ray bands appears, while no significant correlation between the optical and X-ray band was observed. We argue that the emission from Mrk 421 may originate from two different components. One is a steady component from the outer region, which is mainly attributed to the optical band, in which the electrons are accelerated by first-order Fermi acceleration mechanism. We used a steady electron spectrum to produce the SSC emission. The other is a variable component from the inner region, in which the electrons are accelerated by a stochastic acceleration process. We used the timedependent SSC model to produce the emission from the variable component. We suggest that the flares are due to a hardening of the electron spectrum under the process of stochastic acceleration, which leads to a hardening of the observed spectrum in the X-ray and γ-ray bands. Furthermore, we find that the energy densities of electrons and magnetic fields are at near equipartition in both jet regions.