Related papers: X-Ray spectra from protons illuminating a neutron …
It is anticipated that mass accretion rates exceeding approximately $10^{19}\,{\rm g\,s^{-1}}$ in X-ray pulsars lead to radiation-driven outflows from super-critical accretion discs. The outflows launched from the disc influence the angular…
The dynamics and structure of toroidal obscuration around AGN remain uncertain and controversial. In this paper we extend earlier work on the dynamical role of infrared radiation pressure by adding the effects of two kinds of distributed…
Multiwavelength flares from tidal disruption and accretion of stars can be used to find and study otherwise dormant massive black holes in galactic nuclei. Previous well-monitored candidate flares are short-lived, with most emission…
Precision measurements of neutron star radii can provide a powerful probe of the properties of cold matter beyond nuclear density. Beginning in the late 1970s it was proposed that the radius could be obtained from the apparent or inferred…
We calculate the flux and spectrum of \gamma-rays emitted by a two-temperature advection-dominated accretion flow (ADAF) around a black hole. The \gamma-rays are from the decay of neutral pions produced through proton-proton collisions. We…
The luminosity of X-ray pulsars powered by accretion onto magnetized neutron stars covers a wide range over a few orders of magnitude. The brightest X-ray pulsars recently discovered as pulsating ultraluminous X-ray sources reach accretion…
The hydrogen and helium accreted by X-ray bursting neutron stars is periodically consumed in runaway thermonuclear reactions that cause the entire surface to glow brightly in X-rays for a few seconds. With models of the emission, the mass…
A phenomenological model of X-ray variability of accreting black holes is considered, where the variable emission is attributed to multiple active regions/perturbations moving radially towards the central black hole. The hard X-rays are…
The spectra of disc accreting neutron stars generally show complex curvature, and individual components from the disc, boundary layer and neutron star surface cannot be uniquely identified. Here we show that much of the confusion over the…
Popular models for the formation of X-ray spectra in AGN assume that a large fraction of the disk's angular momentum dissipation takes place in a hot corona that carries a small amount of the accreting mass. Here I discuss the formation of…
A BeppoSAX survey of bright Neutron Star (NS) systems in globular clusters, together with the results obtained on Galactic LMXRB, suggests that a two-component model is a reasonable description of the 0.1-200 keV spectra. At energies lower…
We compute the hard X-ray spectra from a hot plasma pervaded by small cold dense clouds. The main cooling mechanism of the plasma is Compton cooling by the soft thermal emission from the clouds. We compute numerically the equilibrium…
XMM-Newton observations of the polar SDSSJ155331.12+551614.5 reveal that all the X-ray flux emerges at energies less than 2 keV. The best fit to the spectrum is with a thermal plasma with kT=0.8 keV plus a 20-90 ev black body, yielding a…
Thermal states of neutron stars in soft X-ray transients (SXRTs) are thought to be determined by "deep crustal heating" in the accreted matter that drives the quiescent luminosity and cooling via emission of photons and neutrinos from the…
It has been recently discovered that the transition of X-ray pulsars to the low luminosity state ($L\lesssim10^{35}\,{\rm erg\,s^{-1}}$) is accompanied by a dramatic spectral change. Namely, the typical power-law-like spectrum with high…
Recent studies of the cosmic X-ray background (XRB) have suggested the possible existence of a population of relatively faint sources with hard X-ray spectra; however, the emission mechanism remains unclear. If the hard X-ray emission is…
Strongly magnetized, accreting neutron stars show periodic and aperiodic variability over a wide range of time scales. By obtaining spectral and timing information on these different time scales, we can have a closer look into the physics…
Emission spectra of hot accretion disks characteristic of advection dominated accretion flow (ADAF) models are investigated for comparison with the brightest ultra-luminous source, X-1, in the galaxy M82. If the spectral state of the source…
We systematically analyze all the available X-ray spectra of disc accreting neutron stars (atolls and millisecond pulsars) from the RXTE database. We show that while these all have similar spectral evolution as a function of mass accretion…
The results of a spectral analysis, using {\it XMM-Newton} and {\it Chandra} data of the brightest ultra luminous X-ray source in the nearby galaxy M82, are presented. The spectrum of M82 X-1, was found to be unusually hard (photon spectral…