XMM-Newton observation of PG 0844 + 349

Abstract

In a ~ 20 ksec XMM-Newton observation the X-ray transient radio-quiet quasar PG 0844+349 was found in a historically high state compared to previous X-ray observations. The quasar showed a featureless spectrum with a strong soft excess over the extrapolation of a hard power law. Comptonization models or a broken power law with Gamma_{soft} ~ 2.75, Gamma_{hard} ~ 2.25 and a break energy of E_{break} ~ 1.35 keV represent acceptable descriptions of the spectral continuum. In the Comptonization models the temperature of the Comptonizing gas is considerably lower than generally found in (broad line) Seyfert galaxies whereas the optical depth is much higher. As a similar behavior has been seen in NLSy1 galaxies, it might be an indicator of the different physical conditions in these two classes of AGN. During the XMM-Newton observation the flux of PG 0844+349 varied achromatically in a smooth, nearly linear fashion, by ~ 25 % on time scales of a few thousand seconds, which puts some constraints on current models of Comptonizing accretion disk coronae.

arXiv comment7 pages, 4 figures. A&A accepted

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• Are Optically-Selected Quasars Universally X-Ray Luminous? X-Ray/UV Relations in Sloan Digital Sky Survey Quasars
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