Gamma ray flares from active region within inhomogeneous AGN jet

Abstract

Two stages of non-thermal emission from relativistic jets in active galaxies can be distinguished: a low level persistent emission and a high level variable emission. It has been recently proposed that both stages are produced in the inner (parsec scale) jet region where electrons are accelerated to TeV energies. We consider a scenario in which the low-level persistent emission originates in the extended, parsec-scale jet but the high level emission is produced by electrons accelerated in a localized region within the inner jet. Our aim is to calculate self-consistently the non-thermal emission expected from the AGN jet in different radiation stages. Then, we will be able to model different emission stages observed in blazars in terms of a single scenario. We modify the stationary, non-local, inhomogeneous AGN jet model for the stationary jet emission by introducing a small active region within the stationary jet, whose physical parameters differ significantly from those in the extended large-scale jet. We distinguish four different emission components which are due to the interaction of relativistic electrons in the active region with the radiation from the active region and radiation from the extended jet and also due to the electrons in the extended jet, which comptonize synchrotron radiation from the extended jet and the active region. Depending on the nature of the active region, we are able to explain the appearance of different types of emission levels in BL Lac type blazars, i.e. the high states observed only in the X-rays or only in the γ-rays. Moreover, we predict the existence of a new type of high emission state in BL Lacs, so called the orphan MeV-soft synchrotron state, in which the inverse Compton emission is mainly limited to the MeV energy range. Such type of blazars have not been observed up to now due to the limited sensitivity of telescopes in the MeV energy range.