We present the identification of the optical counterparts to the low-mass X-ray binaries 1A 1246−588 and 4U 1812−12. We determine the X-ray position of 1A 1246−588 from ROSAT /PSPC observations and find within the error circle a blue star with V = 19.45, B − V = 0.22 and R − I = 0.22 which we identify as the counterpart. Within the Chandra error circle of 4U 1812−12, a single star is present wh...

X-ray spectral state transitions are a key signature of black hole X-ray binaries and follow a well-defined pattern. We examined 12 XMM-Newton observations of the nearby spiral galaxy NGC 1313, which harbors two compact ultraluminous X-ray sources (ULXs), X-1 and X-2, in order to determine if the state transitions in ULXs follow the same pattern. For both sources, the spectra were adequately fi...

The PSR 1259{63 system is unique in that it is the rst radio pulsar found to be in a binary system with a massive main sequence companion. As such, it may be the evolutionary missing link connecting the radio pulsars to the X-ray emitting Be binaries. In this paper, we consider the conditions under which PSR 1259{63 may be the progenitor of the less eccentric, more slowly rotating X-ray Be bina...

In the 35 years since the first X-ray binary was optically identified (Sco X-1) the basic division of X-ray binaries into high-mass X-ray binaries (HMXBs) and low-mass X-ray binaries (LMXBs) has become firmly established. The nomenclature refers to the nature of the mass donor, with HMXBs normally taken to be ≥10M ⊙ , and LMXBs ≤1M ⊙. However, the last decade has seen the identification and mea...