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

P. Giommi, M. Perri, M. Capalbi, V. D'Elia, U. Barres de Almeida, C. H. Brandt, A. M. T. Pollock, F. Arneodo, A. Di Giovanni, Y. L. Chang, O. Civitarese, M. De Angelis, C. Leto, F. Verrecchia, N. Ricard, S. Di Pippo, R. Middei, A. V. Penacchioni, R. Ruffini, N. Sahakyan, D. Israyelyan, S. Turriziani

Published 2021-08-16Version 1

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.