INTEGRAL and Swift Observations of Blazars in Outburst

TL;DR

This paper presents multiwavelength observations of blazars using INTEGRAL and Swift, testing jet-based internal shock models to explain their variability, with successful modeling for some sources but not all.

Contribution

It introduces a model of blazar variability based on internal shocks within jets, tested against new multiwavelength data from INTEGRAL and Swift.

Findings

Model reproduces gamma-ray spectra well for 3C 454.3 and PKS 0537-441.

Internal shock model explains variability in some blazars.

PKS 2155-304 variability is due to different mechanisms.

Abstract

The blazars 3C 454.3, PKS 0537-441 and PKS 2155-304 are traditionally known to be among the most active sources of this class. They emit at all frequencies, up to the gamma-rays, and are good probes of multiwavelength nuclear variability. The first two have also luminous broad emission line regions. We have recently monitored them with various facilities, including Swift and INTEGRAL, and have interpreted their variations with models of non-thermal radiation from a relativistic jet. In particular, we have tested for the first two sources the hypothesis that the variability is produced within the jet through internal shocks, i.e. collisions of relativistic plasma blobs. This allows a parameterization of all physical quantities as functions of the bulk Lorentz factor. We have made the critical assumption that every flaring episode is characterized by a fixed amount of energy. The model reproduces brilliantly the multiwavelength data and especially the gamma-ray spectra, when available. The model is not applicable to PKS 2155-304, the variability of which is caused by independent variations of few individual parameters.