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Based on a spectral analysis of the X-ray continuum, we conclude that the compact primary of the binary X-ray source GRS 1915+105 is a rapidly-rotating Kerr black hole. We find a lower limit on the dimensionless spin parameter of a * > 0.98. Our result is robust in the sense that it is independent of the details of the data analysis and insensitive to the(More)
We consider height-integrated equations of an advection-dominated accretion flow (ADAF), assuming that there is no mass outflow. We include convection through a mixing length formalism. We seek self-similar solutions in which the angular velocity and sound speed scale as R −1/2 , where R is the radius, and consider two limiting prescriptions for the(More)
It is proposed that gamma-ray bursts are created in the mergers of double neutron star binaries and black hole neutron star binaries at cosmological distances. Bursts with complex profiles and relatively long durations are the result of magnetic flares generated by the Parker instability in a post-merger differentially-rotating disk. Some bursts may also be(More)
Active galactic nuclei, x-ray binaries, pulsars, and gamma-ray bursts are all believed to be powered by compact objects surrounded by relativistic plasma flows driving phenomena such as accretion, winds, and jets. These flows are often accurately modelled by the relativistic magnetohydrodynamics (MHD) approximation. Time-dependent numerical MHD simulations(More)
As the luminosity of an accreting black hole drops to a few percent of Eddington, the spectrum switches from the familiar soft state to a hard state that is well-described by a distended and tenuous advection-dominated accretion flow (ADAF). An ADAF is a poor radiator, and the ion temperature can approach 10 12 K near the center, although the electrons are(More)
We fit X-ray spectral data in the thermal dominant or high soft state of two dynamically confirmed black holes, GRO J1655-40 and 4U 1543-47, and estimate the dimensionless spin parameters a * ≡ a/M of the two holes. Our spectral model consists of one principal component, a multitemperature blackbody disk model that includes all general relativistic effects,(More)
We present a model for the anomalous X-ray pulsars (AXPs) in which the emission is powered by accretion from a fossil disk, established from matter falling back onto the neutron star following its birth. The time-dependent accretion drives the neutron star towards a " tracking " solution in which the rotation period of the star increases slowly, in tandem(More)