| Name: | Sandeep Rout |
| Affiliation: | Physical Research Laboratory, Ahmedabad |
| Conference ID : | ASI2022_141 |
| Title : | Spectral and temporal evolution of Cyg X-1 during 2016-17 state transition as observed with AstroSat |
| Authors : | Sandeep K. Rout, Santosh Vadawale, et al. |
| Abstract Type: | Poster |
| Abstract Category : | Stars, ISM and Galaxy |
| Abstract : | The X-ray properties of the prototypical black hole source Cygnus X-1 shows marked differences from low-mass X-ray binaries (LMXB). It is a persistent source remaining mostly in a hard powerlaw-dominated state and while transitioning to a softer state it never goes to the canonical high/soft state. There is always a significant fraction of Comptonized flux in the total spectrum and the fractional rms also remains at a much higher (about 20 per cent) level during soft states. Also, the power spectra of Cygnus X-1 never shows quasi periodic oscillations (QPO). Instead, they display a number of broad peaks spanning several orders of magnitude in frequency. Here, I will present the results of a comprehensive spectral and timing analysis of Cygnus X-1 using 21 sets of broadband X-ray data from AstroSat observed during the 2016-17 state transition with an objective to uncover some of these mysteries. We find that the state transition most likely takes place because of the inward movement of the disk. With the help of correlation studies between spectral and temporal properties we find that one of the broad peaks in the power spectra is very similar to the Type C QPO. We further modeled the rms and lag spectra of these broad peaks to confirm that the radiative origin of this peak can be explained by oscillations in the Comptonization medium or the corona similar to QPOs in LMXBs. We are also able to constrain the physical extent of the corona and its variation during the state transition. |