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

We present XMM-Newton observations of the 569-s-period system RX J1914+24 (V407 Vul). This period is believed to represent the binary orbital period making it an ultracompact binary system. By comparing the phase of the rise to maximum X-ray flux at various epochs (this includes observations made using ROSAT, ASCA and Chandra) we find that the system is spinning up at a rate of 3.17 +/- 0.07 × 10^-12ss^-1. We find that the spectra soften as the X-ray flux declines towards the off-phase of the 569-s period. Further, the spectra are best fitted by an absorbed blackbody component together with a broad emission feature around 0.59 keV. This emission feature is most prominent at the peak of the on-phase. We speculate on its origin.