XMM-Newton and Chandra observations of the ultra-compact binary RX J1914 + 24

Abstract

The nature of the X-ray source RX J1914 + 24 has been the subject of much debate. It shows a prominent period of 569 s in X-rays and the optical/infrared: in most models this has been interpreted as the binary orbital period. We present our analysis of new XMM-Newton and Chandra data. We find a longer term trend in the XMM-Newton data and power at 553 and 584 s in five sets of data. It is not clear if they are produced as a result of a beat between a longer intrinsic period and the 569-s modulation or if they are due to secular variations. We obtain a good fit to the XMM-Newton spectrum with a low-temperature thermal plasma model with an edge at 0.83 keV. This model implies an unabsorbed bolometric X-ray luminosity of 1 × 10³³erg s^-1 (for a distance of 1 kpc) - this is 2 orders of magnitude lower than our previous estimate (derived using a different model). If the distance is much less, as the absorption derived from the X-ray fits suggest, then the X-ray luminosity is even lower at ~ 3 × 10³¹erg s^-1.