Astronomy and Astrophysics Seminars

Current observational understanding of the accretion geometry [from stellar mass black hole to AGN] using temporal analysis

by Dr. Mayukh Pahari (University of Southampton, UK)

Thursday, January 10, 2019 from to (Asia/Kolkata)
at A269
Description
Observations from the current state-of-art instruments, the structure of the accretion disc around black holes, from the X-ray binaries (BHXBs) to the Active Galactic Nuclei (AGN) are found to be more complicated than it is previously thought. Two key reasons are (1) the departure of the observational accretion disc from the "geometrically-thin disk" assumption at high luminosity and (2) the uncertainty on the geometry of the dominant hard X-ray emitting region. Spectroscopic measurements are considered to play a crucial role in addressing these two issues, but they are often found to be degenerate given the complexity of the radiation mechanism. On the other hand, time-series analysis which involves technique like delay measurements in emissions at different wavelengths is proven to be robust and insightful to provide a more accurate description of the accretion geometry. In this presentation, I shall give a brief overview of the latest results that boost our understanding of the accretion disc structure and discuss results from my current research involving spectro-temporal analysis of BHXBs and AGN. Applying time-series analysis techniques on multiwavelength observations involving instruments like Swift, XMM-Newton, IUE, we found that accretion disc requires a thick, vertical structure at high accretion rate. Using high-quality observations, we can narrow down the uncertainties on the geometry of the hard X-ray emitting regions. I shall discuss the implications of our results in the light of accretion disc models.