2XMMi J225036.9+573154 - a new eclipsing AM Her binary discovered using XMM-Newton

TL;DR

This paper reports the discovery of a new eclipsing polar binary system using X-ray observations from XMM-Newton, revealing unique features like continuous X-ray emission outside eclipses and specific absorption dips.

Contribution

First identification of an eclipsing polar with continuous X-ray emission and detailed characterization of its orbital and spectral properties.

Findings

Total eclipse of white dwarf every 174 mins

Presence of pre-eclipse absorption dip in soft X-rays

X-ray emission observed at all orbital phases except during eclipse

Abstract

We report the discovery of an eclipsing polar, 2XMMi J225036.9+573154, using XMM-Newton. It was discovered by searching the light curves in the 2XMMi catalogue for objects showing X-ray variability. Its X-ray light curve shows a total eclipse of the white dwarf by the secondary star every 174 mins. An extended pre-eclipse absorption dip is observed in soft X-rays at phi=0.8-0.9, with evidence for a further dip in the soft X-ray light curve at phi~0.4. Further, X-rays are seen from all orbital phases (apart from the eclipse) which makes it unusual amongst eclipsing polars. We have identified the optical counterpart, which is faint (r=21), and shows a deep eclipse (>3.5 mag in white light). Its X-ray spectrum does not show a distinct soft X-ray component which is seen in many, but not all, polars. Its optical spectrum shows Halpha in emission for a fraction of the orbital period.