An XMM–Newton observation of the symbiotic star AG Peg: the X-ray emission after the end of its 2015 outburst.

We present an analysis of the XMM–Newton observation of the symbiotic star AG Peg, obtained after the end of its 2015 outburst. The X-ray emission of AG Peg is soft and of thermal origin. AG Peg is an X-ray source of class β of the X-ray sources among the symbiotic stars, whose X-ray spectrum is well matched by a two-temperature optically thin plasma emission (kT 1∼ 0.14 keV and kT 2∼ 0.66 keV). The X-ray emission of the class β sources is believed to originate from colliding stellar winds (CSWs) in a binary system. If we adopt the CSW picture, the theoretical CSW spectra match well the observed properties of the XMM–Newton spectra of AG Peg. However, we need a solid evidence that a massive-enough hot-star wind is present in the post-outburst state of AG Peg to proof the validity of the CSW picture for this symbiotic binary. No short-term X-ray variability is detected while the UV emission of AG Peg shows stochastic variability (flickering) on time-scales of minutes and hours. [ABSTRACT FROM AUTHOR]