RX J1914.4 + 2456: The first double-degenerate polar?

Abstract

RX J1914.4 + 2456 exhibits a light curve with a strong modulation at 569 s: this period is characteristic of the white dwarf spin period in intermediate polar (IP) systems. However, the X-ray light curve is difficult to reconcile with current models for IP emission. We argue that a simpler explanation is that the system is a polar with a degenerate secondary star, which would make it the first known system of its kind. As such it should contain the first example of an He-dominated radial accretion flow on to the white dwarf surface, and RX J1914.4 + 2456 would have the shortest known orbital period of any binary system.