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 (kT₁ ∼ 0.14 keV and kT₂ ∼ 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.