Abstract
In March 2009 the well-studied quasar, PG 0844+349, was discovered with Swift to be in an X-ray weak state. A follow-up XMM-Newton observation several weeks later generated a good quality spectrum of the source, showing substantial curvature and spectral hardening. In combination with archival data at two previous epochs when the source was in a bright state, we examine the long-term spectral and timing properties of PG 0844+349 spanning nearly ten years and a factor of ten in brightness. Partial covering and blurred reflection models are compared to the data at each flux state while attempting to maintain consistency between the various epochs. In terms of the blurred reflection model, PG 0844+349 is in a reflection dominated state during the 2009 X-ray weak observations, which can be understood in terms of light bending. Moreover, the light bending scenario can also account for the short-term (i.e. ~1000s) spectral variability in the source. Other models cannot be decisively ruled out, but we note distinguishing features of the models that can be explored for in higher signal-to-noise data from current and future observatories.
Highlights
The X-ray spectra of active galactic nuclei (AGNs) can exhibit such significant differences from one epoch to the that it can become very difficult to extract meaningful constraints from single-epoch spectra
As it was found to be so, an XMM–Newton Target of Opportunity (ToO) was triggered a few days later and it is these new data, in combination with the previous XMM–Newton observations, that we report on here
Reflection from an ionized disc blurred for relativistic effects close to the black hole is often adopted to describe the origin of the soft excess (Ballantyne, Ross & Fabian 2001; Ross & Fabian 2005), and has been successfully fitted to the spectra of unabsorbed AGN (e.g. Fabian et al 2004; Crummy et al 2006; Ponti et al 2010; Zoghbi et al 2010)
Summary
The X-ray spectra of active galactic nuclei (AGNs) can exhibit such significant differences from one epoch to the that it can become very difficult to extract meaningful constraints from single-epoch spectra. One attractive proposition is to catch AGN in a low X-ray flux state (Gallo 2006). Efforts to identify objects in the low X-ray flux state by monitoring AGNs with Swift and triggering a pointed XMM–Newton observation when an object is discovered to be in a low state are proving advantageous Pounds et al (2003) reported absorption features in this same data set that they interpreted as high-mass, relativistic outflows. A subsequent reanalysis of the data along with a deeper observation by Brinkmann et al (2006) could not confirm the absorption features reported by Pounds et al and attributed them to calibration uncertainties (see Vaughan & Uttley 2008).
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