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High Mass X-ray Binaries (HMXBs) are interesting objects that provide a wide range of observational probes to the nature of the two stellar components, accretion process, stellar wind and orbital parameters of the systems. A large fraction…
We study the formation of low-mass black hole X-ray binaries with main sequence companions that have formed through case C mass transfer (mass transfer following the helium core burning phase of the black hole progenitor). We identify these…
The majority of the ultraluminous X-ray sources (ULXs) in external galaxies are believed to be accreting black holes in binary systems; some of the black holes could be as massive as $\sim 100-1000 \ms$. We have performed evolution…
Recent X-ray observations have detected a class of very faint X-ray transients in the Galaxy which probably reveal a previously unrecognised type of accretion on to neutron stars or black holes. We show that these systems cannot have…
Galactic binary systems that contain a black hole candidate emit hard X-rays in their low luminosity mode. We show that this emission can be understood as due to the Compton scattering of photons from the companion star and/or the accretion…
Very faint X-ray binaries appear to be transient in many cases with peak luminosities much fainter than that of usual soft X-ray transients, but their nature still remains elusive. We investigate the possibility that this transient…
The properties of X-ray emission from accreting black holes are reviewed. The contemporary observational picture and current status of theoretical understanding of accretion and formation of X-ray radiation in the vicinity of the compact…
According to the paradigm of solar-type dynamo action brown dwarfs should not exhibit magnetic activity as they are fully convective. Indeed, Halpha observations of ultracool field dwarfs indicate a decline of activity setting in near the…
The phenomenology of a subclass of High Mass X-ray Binaries hosting a blue supergiant companion, the so-called Supergiant Fast X-ray Transients (SFXTs), is reviewed. Their number is growing, mainly thanks to the discoveries performed by the…
We report on the optical detection of the black hole X-ray transient MAXI J1659-152 during its quiescent state. By using the Canada France Hawaii Telescope (CFHT), we observed MAXI J1659-152 about 7 months after the end of an X-ray…
A new, transient ultraluminous X-ray source (ULX) was recently discovered by Chandra in M31 with a luminosity at ~ 5 x 10^39 erg/s. Here we analyse a series of five subsequent XMM-Newton observations. The steady decline in X-ray luminosity…
The last two decades have seen a great improvement in our understand- ing of the complex phenomenology observed in transient black-hole binary systems, especially thanks to the activity of the Rossi X-Ray Timing Explorer satellite, com-…
The dynamical production of low-mass X-ray binaries and brighter cataclysmic variables (CVs) in dense globular clusters is well-established. We investigate how the X-ray emissivity of fainter X-ray binaries (principally CVs and coronally…
We have carried out a deep search at 1.4 GHz for radio pulsed emission from six soft X-ray transient sources observed during their X-ray quiescent phase. The commonly accepted model for the formation of the millisecond radio pulsars…
Using the RossiXTE experiment, we detect weak X-ray emission from the recurrent Be/X-ray transient A 0535+26 at a time when the optical counterpart V725 Tau displayed H-alpha in absorption, indicating the absence of a circumstellar disc.…
X-ray appearance of normal galaxies is mainly determined by X-ray binaries powered by accretion onto a neutron star or a stellar mass black hole. Their populations scale with the star-formation rate and stellar mass of the host galaxy and…
We have observed the soft X-ray transient XTE J0421+56 in quiescence with XMM-Newton. The observed spectrum is highly unusual being dominated by a broad feature at 6.5 keV and can be modeled by a strongly absorbed continuum. The spectra of…
Two X-ray sources were recently discovered by Irwin et al. in compact companions to elliptical galaxies to show ultra-luminous flares with fast rise (~ minute) and decay (~ hour), and with a peak luminosity ~10^{40-41} erg/s. Together with…
In this paper we survey the theory of wind accretion in high mass X-ray binaries hosting a magnetic neutron star and a supergiant companion. We concentrate on the different types of interaction between the inflowing wind matter and the…
X-ray binaries are binary star systems in which a compact object (a neutron star or a black hole) and a relatively normal star orbit a common centre of mass. Since the discovery of X-ray binaries with the first X-ray telescopes in the…