Type I X-ray bursts are very common in neutron star X-ray binaries, but no Type I bursts have been seen in the dozen or so binaries in which the accreting compact star is too massive to be a neutron star and therefore identified as a black hole candidate. If these black hole candidates had surfaces, we show that they would very likely have exhibited burst behavior. We discuss how the lack of bu...

The gamma-ray observatory INTEGRAL, launched in October 2002, produces a wealth of discoveries and new results on compact high energy Galactic objects, nuclear gammaray line emission, diffuse line and continuum emission, cosmic background radiation, AGN and high energy transients. Two important serendipitous discoveries made by the INTEGRAL mission are new classes of X-ray binaries, namely the ...

Ultracompact X-ray binaries (UCXBs) appear able to sustain accretion onto the compact accretor at rates lower than in wider X-ray binaries. This may be understood by the smaller accretion disks in UCXBs: a lower X-ray luminosity suffices to keep a disk completely ionized through irradiation and, thus, keep the viscosity at a sufficiently high level to allow effective transport of matter to the ...

We report on X-ray properties of the gamma-ray binary 1FGL J1018.6−5856 using observations obtained with the Swift X-ray telescope. Using 54 observations made between MJD 55575 and 55984, we find that the X-ray flux is modulated at a period of 16.57 ± 0.11 days, consistent with previous reports based on gamma-ray data. We find that the X-ray maximum at phase 0 previously reported may not be a p...

We present model X-ray spectra of accreting black holes with advection-dominated accretion flows, paying attention to thermal emission lines from the hot plasma. We show that the Advanced X-ray Astrophysical Facility (AXAF) might be able to observe lines from X-ray binaries such as V404 Cyg in quiescence, the Galactic center black hole Sagittarius A, and the nuclei of nearby galaxies such as M8...

We study a Chandra X-ray Observatory ACIS-S observation of the Galactic globular cluster M12. With a 26 ks exposure time, we detect 6 X-ray sources inside the half-mass radius (2.16) of which two are inside the core radius (0.72) of the cluster. If we assume these sources are all associated with globular cluster M12, the luminosity LX among these sources between 0.3-7.0 keV varies roughly from ...