| 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.
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