The changing look of PKS 2149-306
Tagliaferri, G.; Ghisellini, G.; Pian, E.; Wolter, A.; Tavecchio, F.; Foschini, L.; Di Cocco, G.; Treves, A.; Bianchin, V.; Gliozzi, M.; Sambruna, R. M.
Italy, United States
Abstract
Aims: We study the blazar nature of the high-redshift Flat-Spectrum Radio Quasar PKS 2149-306 (z = 2.345) by investigating its long-term behavior.
Methods: We analyzed all publicly available optical-to-X-ray observations performed by XMM-Newton, Swift, and INTEGRAL.
Results: PKS 2149-306 is one of four blazars at z > 2 that have been observed in the hard-X-ray regime with both the BAT and ISGRI instruments. Observations acquired almost 1 year apart in the 60{-}300 keV energy band in the object rest frame, exhibit no noticeable change in spectral slope associated with a flux variation of more than a factor of two. Swift data appear to show a roll-off below 1 keV, which becomes increasingly evident during a 3-day time-frame, that can be explained as the natural spectral break caused by the Inverse Compton onset. The broad-band spectra allow us to identify two different states. The SED modeling suggests that they can be interpreted by only a change in the bulk Lorentz factor of the jet.