arXiv subjects

Abhas Mitra

Publications and source records attributed to Abhas Mitra.

56 records · Page 4Linked to original sources

arXiv1998

No Massive Black-Hole in Cygnus X-3

There has been a recent suggestion that Cyg X-3 contains a black hole (BH) of mass ~17 solar mass. This interpretation is closely linked to a previous claim that Cyg X-3 contains a Wolf-Rayet star of mass ~ 10 solar mass. The latter interpretation would imply that the X-ray source in this close binary (P = 4.8 hr) is enshrouded by a relatively cool superstrong wind > 10^{-5} solar mass/yr. It can be shown that such a wind would be completely opaque to the low energy X-rays observed from the source and hence the Wolf-Rayet hypothesis can not be a correct one. By pursuing the same argument it also follows that the compact object must be of modest mass ruling out the existence of a massive BH in Cyg X-3. Note, however, that at present we can not strictly rule out the probable existence of stellar mass BH in Cyg X-3 or any other X-ray binary which are believed to contain a neutron star as the compact object. Yet, a more probable scenario for Cyg X-3 would be one where the compact object is a canonical neutron star (NS) and the companion is an extremely low mass dwarf, ~0.001 solar mass, much like PSR 1957+20.

astro-ph↗

arXiv1997

The Expected Duration of Gamma-Ray Bursts in the Impulsive Hydrodynamic Models

Depending upon the various models and assumptions, the existing literature on Gamma Ray Bursts (GRBs) mentions that the gross theoretical value of the duration of the burst in the hydrodynamical models is tau~r^2/(eta^2 c), where r is the radius at which the blastwave associated with the fireball (FB) becomes radiative and sufficiently strong. Here eta = E/Mc^2, c is the speed of light, E is initial lab frame energy of the FB, and M is the baryonic mass of the same (Rees and Meszaros 1992). However, within the same basic framework, some authors (like Katz and Piran) have given tau ~ r^2 /(eta c). We intend to remove this confusion by considering this problem at a level deeper than what has been considered so far. Our analysis shows that none of the previously quoted expressions are exactly correct and in case the FB is produced impulsively and the radiative processes responsible for the generation of the GRB are sufficiently fast, its expected duration would be tau ~ar^2/(eta^2 c), where a~O(10^1). We further discuss the probable change, if any, of this expression, in case the FB propagates in an anisotropic fashion. We also discuss some associated points in the context of the Meszaros and Rees scenario.

astro-ph↗