Diffuse 511 keV line emission, from the annihilation of cold positrons, has been observed in the direction of the Galactic Centre for more than 30 years. The latest high-resolution maps of this emission produced by the SPI instrument on INTEGRAL suggest at least one component of the emission is spatially coincident with the distribution of ∼70 luminous, low-mass X-ray binaries detected in the s...

We searched for X-ray bursts in XMM-Newton archival data of X-ray sources in M 31 globular clusters (GCs) and GC candidates. We detected two bursts simultaneously in EPIC pn and MOS detectors and some more candidates in EPIC pn. The energy distribution of the burst photons and the intrinsic luminosity during the peak of the bursts indicate that at least the strongest burst was a type I radius e...

From hot, tenuous gas dominated by Compton processes, to warm, photoionized emission-line regions, to cold, optically thick fluorescing matter, accreting gas flows in X-ray binaries span a huge portion of the parameter space accessible to astrophysical plasmas. The coexistence of such diverse states of material within small volumes (10–10 cm) leaves X-ray spectroscopists with a challenging set ...

Using X-ray monitoring observations with the All Sky Monitor (ASM) on board the Rossi X-ray Timing Explorer (RXTE) and the Burst Alert Telescope (BAT) on board the Swift, we are able to study the spectral state transitions occurred in about 20 bright persistent and transient black hole and neutron star binaries. We have confirmed that there is a correlation between the X-ray luminosity correspo...

Using King-Mitchie Models, we compute encounter rates between the various stellar species in the globular clusters ! Cen, and 47 Tuc. We also compute event rates for encounters between single stars and a population of primordial binaries. Using these rates, and what we have learnt from hydrodynamical simulations of encounters performed earlier, we compute the production rates of objects such as...

The importance of stellar encounters in producing stellar exotica in dense stellar clusters is reviewed. We discuss how collisions between main–sequence stars may be responsible for the production of blue stragglers in globular clusters. We also discuss the possible pathways to the production of X–ray binaries, cataclysmic variables, and millisecond pulsars in globular clusters. Neutron stars i...

Recent deep Chandra surveys of the Galactic center region have revealed the existence of a low luminosity hard X-ray point source population. It has been proposed that a majority of these sources can be explained by main sequence neutron star (MS-NS) binary systems in which the neutron stars are fed by a stellar wind. In this investigation, a population synthesis study of the Galactic center re...

X-ray bursts from bright sources in globular clusters of our galaxy show that at least 11 (of a total 13) of these sources are neutron stars. One of the low-luminosity X-ray sources in ω Cen is a neutron star accreting at a low rate. Together with the discoveries that M 15 contains two bright X-ray sources, and that 47 Tuc and NGC 6440 contain 2 and 5 low-luminosity X-ray sources with a neutron...

We analyzed archival Chandra X-ray observations of the central portion of the 30 Doradus region in the Large Magellanic Cloud. The image contains 20 X-ray point sources with luminosities between 5× 10 and 2× 10 erg s (0.2 – 3.5 keV). A dozen sources have bright WN Wolf-Rayet or spectral type O stars as optical counterparts. Nine of these are within ∼ 3.4 pc of R 136, the central star cluster of...

We report the discovery of several optical burst-like events from the low-mass X-ray binary MS 1603.6+2600 (UW CrB). The events last for a few tens of seconds, exhibit a very fast rise and slow decay, and involve optical brightening of a factor of 2–3. The flares appear distinct from the lower level flickering and instead strongly resemble reprocessed type-I X-ray bursts as seen in a number of ...