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

TL;DR

This paper analyzes XMM-Newton X-ray observations of the symbiotic star AG Peg after its 2015 outburst, revealing soft, thermal X-ray emission consistent with colliding stellar winds, but lacking short-term variability.

Contribution

It provides the first detailed X-ray spectral analysis of AG Peg post-outburst, supporting the colliding stellar winds model with spectral fitting.

Findings

X-ray emission is soft and thermal, matching two-temperature plasma models.

Spectral data aligns with colliding stellar winds theory.

No short-term X-ray variability detected, but UV flickering observed.

Abstract

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 beta of the X-ray sources amongst 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 beta sources is believed to originate from colliding stellar winds (CSW) in 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.