Abstract Details
| Name: Nagendra Kumar Affiliation: Ph.D. student, IUCAA, Pune-411007 Conference ID: ASI2016_833 Title : Inferring the possible geometry of the Comptonizing system in NS LMXBs & Time-lags associated to Comptonization process, a Monte Carlo study. Authors and Co-Authors : Prof. Ranjeev Misra Abstract Type : Poster Abstract Category : Stars, The Milky Way Galaxy and its neighbours Abstract : The observed soft lags of kHZ QPOs in neutron star (NS) low-mass X-ray binaries (LMXBs) is explained, generally, in thermal Comptonization (TC) model when one consider the affect of some fraction of Comptonized photons ($\eta_e$) which impinge back to the source. This fraction depends naturally on the geometry of the system and this involves, tracing photons as the scatter in space. A Monte Carlo (MC) method is developed for the thermal Comptonization process. We computed the fraction $\eta_e$ for different geometries as well the fraction of photons which will impinge back on the accretion disk $\eta_{irr}$. Three geometries were considered: (i) where the corona is a spherical shell covering the input source along with the possibility that there is a gap between the two i.e. a hollow shell, (ii) where the corona is in the form of a boundary layer and (iii) where the corona exists above the accretion disk. We find that the $\eta_e$ obtained from these geometries roughly correspond to the constraints obtained in the TC models for the first two geometries. In Comptonization, the high energetic photons is generally scattered more comparison to softer ones, so the “hard lag†should be observed. The observed both type of lag `hard' & 'soft' lag associated to X-ray variability are explained due to oscillations in temperature either of seed-photon source ($T_b$), or medium ($T_e$), or combination of them, in TC model. These lags can be explained in a MC methods. We find that when a less then half cycle of temperature is changed during photons crossing time, the lag is hard lag and for more then half cycle the lag is soft. |