AR_final file_2018-19

scribed by a model consisting of a primary X-ray power-law continuum, a blurred reflection compo- nent, Comptonized disc emission as the soft X-ray excess, optical/UV emission from a standard accre- tion disc and a steep power law component, most likely the jet emission in the UV band. ‘ Modelling the energy dependent tem- poral behaviour of Cygnus X-1 In the last two decades, there have been extensive studies on the rapid temporal behaviour of X-ray binaries primarily using Rossi X-ray Timing Ex- plorer (RXTE) data. The X-ray variability of these sources are characterized by their power density spectra (PDS), which show broad band continuum noise like features, and sometimes peaked features known as quasi-periodic oscillations (QPOs). The origin of the broad band continuum noise could be due to perturbations, which occur throughout the disk and propagate inwards causing the X-ray vari- ation. Since these variations occur at different radii and are expected to have a multiplicative effect on the accretion rate of inner disk, the scenario pro- vides an explanation for the linear relationship of the root mean square (rms) variability with the flux. Additionally, the model also makes predictions on energy dependent temporal properties of the sys- tem. In particular, the variation of the fractional rms and time-lag as a function of energy can pro- vide clues to the geometry of the system within this paradigm. Bari Maqbool Bhat , Ranjeev Misra and others have studied the results from six observations of Cygnus X-1 by Large Area X- ray Proportional Counter (LAXPC) and Soft X- ray Telescope (SXT) on-board AstroSat , when the source was in the hard spectral state as revealed by the broad band spectra. The spectra obtained from all the observations can be described by a sin- gle temperature Comptonizing region with disk and reflection components. The event mode data from LAXPC provides unprecedented energy dependent fractional rms and time-lag at different frequencies, which they fit with empirical functions. They in- voked a fluctuation propagation model for a simple geometry of a truncated disk , with a hot inner re- gion. Unlike other propagation models, the hard X-ray emission ( > 4 keV) was assumed to be from the hot inner disk by a single temperature ther- mal Comptonization process. The fluctuations first cause a variation in the temperature of the trun- cated disk and then the temperature of the inner disk after a frequency dependent time delay. They were successful in showing that the proposed model could explain the energy dependent rms and time- lag at different frequencies. (See Figure 14). UV to X–Ray Comptonization delay in Mrk 493 The broadband X–ray emission from Type 1 AGN, dominated by a power–law continuum, is thought to arise from repeated inverse Compton scatter- ing of seed optical/UV photons by energetic elec- trons in a hot corona. The seed optical/UV pho- tons are assumed to arise from an accretion disk, but direct observational evidence has remained elu- sive. Adegoke Oluwashina, Pramod Pawar, Gu- lab C. Dewangan , and Main Pal have reported the first direct observational evidence for the accre- tion disk being responsible for the seed photons for thermal Comptonization in the hot corona based on ∼ 100 ks XMM–Newton observations of the narrow–line Seyfert 1 galaxy Mrk 493. They find that the UV emission leads by ∼ 5 ks relative to the X–ray emission. The UV lead is consistent with the time taken by the UV photons to travel from the location of their origin in the accretion disk to the hot corona, and the time required for repeated inverse Compton scattering converting the UV pho- tons into X–ray photons. AGN feedback in the core of a galaxy cluster A2626 Sonali Kadam, Satish Sonkamble, Pramod Pawar , and Madhav K. Patil have analyzed the publicly available two Chandra observations and 1 . 4 GHz VLA radio data on A2626 to asesses the appropriateness of the AGN heating with the cooling of the ICM on the basis of the radio power of the central black hole. This study confirmed the ( 80 )