1,721,254 research outputs found
X-ray spectral states and metallicity in the ultraluminous X-ray sources NGC 1313 X-1 and X-2
No full textWe present a systematic analysis of the X-ray spectra of NGC 1313 X-1 and NGC 1313 X-2, using three years of XMM-Newton observations. We fitted the continuum with a Comptonization model plus a multicolour blackbody disc, which describes the effects of an accretion disc plus a corona. We checked the consistency of this spectral model on the basis of the variability patterns of its spectral parameters. We found that the two sources show different spectral states. We tentatively interpret the observed behaviour of NGC 1313 X-1 and X-2 within the framework of near-Eddington and/or super-Eddington accretion. We also attempted to determine the chemical abundances in the local environment of NGC 1313 X-1 and X-2 from the EPIC and RGS spectra. The results appear to indicate subsolar metallicity for both sources
Time-dependent Analysis of Spherical Accretion onto Black Holes
No full textResults are presented from a time-dependent, numerical investigation of spherical accretion on to black holes, within the framework of relativistic radiation hydrodynamics. We have studied the stability of self-consistent, stationary solutions of black hole accretion with respect to thermal and radiative perturbations, and also the non-linear evolution of unstable, high-temperature models, heated by the hard radiation produced by the accretion flow itself in the inner region near to the horizon. In some cases, a hydrodynamic shock forms at about 10(3)-10(4) Schwarzschild radii, where Compton heating exceeds radiative cooling. The calculations have been made using a suitably designed radiation hydrodynamics code, in which radiative transfer is handled by means of the PSTF moment formalism and which contains an original treatment of the radiation temperature equation
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