The new object, designated SRGE J075818-612027, most likely belongs to the polar subtype of cataclysmic variables. This is reported in an article published on February 26 on the arXiv preprint server.
Cataclysmic variables (CVs) are binary star systems consisting of a white dwarf accreting material from a normal stellar companion. They unevenly increase the brightness several times, and then return to a state of rest again. Polars are a subclass of cataclysmic variables, distinguished from other CVs by the presence of a very strong magnetic field in their white dwarfs.
Recently, a team of astronomers led by Samet Ok of the Leibniz Institute for Astrophysics in Potsdam, Germany, analyzed data from the open cluster NGC 2516 using the eROSITA X-ray telescope at the Spektr-RG space observatory and TESS. As a result, by a lucky chance, they discovered something new.
“We report the discovery of the object SRGE J075818-612027, which was accidentally discovered in eROSITA observations of the open cluster NGC 2516,” the researchers write in the paper.
SRGE J075818-612027 was identified as one of the brightest X-ray objects during the observation phase of the eROSITA telescope. It turned out that this is a background accretionary object located at a distance of 4000 to 13500 light years.
Further observations of the object SRGE J075818-612027 revealed a period of about 106 minutes. Other results confirmed that SRGE J075818-612027 is a magnetic cataclysmic variable.
According to the study, the X-ray spectrum of SRGE J075818-612027 is compatible with the emission of a single-temperature thermal plasma at a level of about 10 keV, which is typical for polars. In addition, the object exhibits large differences in values over large time scales in both the optical and X-ray wavelength ranges. This behavior can be interpreted as high and low states, further supporting its classification as a polar.
The photo above is an X-ray image of NGC 2516 taken by the eROSITA space telescope. The white dotted circle marks the position of SRGE J075818-612027.
Source: Samet Ok et al, Serendipitous discovery of the magnetic cataclysmic variable SRGE J075818-612027, arXiv (2023). DOI: 10.48550/arxiv.2302.13315
