A serendipitous XMM-Newton observation of MACHO 104.20906.960: A dwarf nova candidate with a 2 h period

Abstract

The binaries known as cataclysmic variables are particular binary systems in which the primary star (a white dwarf) accretes material from a secondary via Roche-lobe mechanism. Usually, these objects have orbital period of a few hours so that a detailed temporal analysis can be performed. Here, we present Chandra and XMM-Newton observations of a dwarf nova candidate identified in the past by optical observations towards the galactic Bulge and labeled as MACHO 104.20906.960. After a spectral analysis, we used the Lomb-Scargle technique for the period search and evaluated the confidence level using Monte-Carlo simulations. In this case, we found that the X-ray source shows a period of 2.03-0.07+0.09 h ( 3σ error) so that it is most likely a system of interacting objects. The modulation of the signal was found with a confidence level of >99%. The spectrum can be described by a two thermal plasma components with X-ray flux in the 0.3-10 keV energy band of 1.77-0.19+0.16×10^-13ergscm. We find that the distance of the source is approximately 1 kpc thus corresponding to a luminosity L_X≃2×10³¹erg s.