X-ray spectra, light-curves and SEDs of blazars frequently observed by Swift

TL;DR

This study compiles and analyzes extensive Swift-XRT data for over 65 blazars, revealing significant X-ray variability, spectral changes, and broad-band SED characteristics, advancing understanding of blazar emission mechanisms.

Contribution

It provides a comprehensive database of X-ray spectra and multi-frequency SEDs for a large sample of blazars, with detailed variability and spectral analysis, which is novel in scope and depth.

Findings

Large X-ray luminosity variability across all objects.

Spectral behavior varies with SED type, showing 'harder-when-brighter' or 'softer-when-brighter' trends.

Significant changes in the synchrotron peak energy, spanning over two orders of magnitude.

Abstract

Blazars research is one of the hot topics of contemporary extra-galactic astrophysics. That is because these sources are the most abundant type of extra-galactic gamma-ray sources and are suspected to play a central role in multi-messenger astrophysics. We have used swift_xrtproc, a tool to carry out an accurate spectral and photometric analysis of the Swift-XRT data of all blazars observed by Swift at least 50 times between December 2004 and the end of 2020. We present a database of X-ray spectra, best-fit parameter values, count-rates and flux estimations in several energy bands of over 31,000 X-ray observations and single snapshots of 65 blazars. The results of the X-ray analysis have been combined with other multi-frequency archival data to assemble the broad-band Spectral Energy Distributions (SEDs) and the long-term light-curves of all sources in the sample. Our study shows that large X-ray luminosity variability on different timescales is present in all objects. Spectral changes are also frequently observed with a "harder-when-brighter" or "softer-when-brighter" behavior depending on the SED type of the blazars. The peak energy of the synchrotron component nu_peak in the SED of HBL blazars, estimated from the log-parabolic shape of their X-ray spectra, also exhibits very large changes in the same source, spanning a range of over two orders of magnitude in Mrk421 and Mrk501, the objects with the best data sets in our sample.