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 ( 3 σ 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 - 13 erg s - 1 cm - 2 . We find that the distance of the source is approximately 1 kpc thus corresponding to a luminosity L X ≃ 2 × 10 31 erg s - 1 .