Deepika Bollimpalli – Variability in discs around black holes: Broadband variability and QPOs

Recording of the seminar at the institute of Physics on the 12th of May 2022

Author: Deepika Bollimpalli

Title: Variability in discs around black holes: Broadband variability and QPOs

Abstract: Long-term observations have shown that black hole X-ray
binaries exhibit strong, aperiodic variability on time scales of a few
milliseconds to seconds. In addition, these systems also exhibit rapid
variability in their X-ray light curves termed quasi-periodic
oscillations (QPOs); also broadly classified into high-frequency and
low-frequency QPOs. Understanding the nature of these variabilities
and the underlying physical processes helps us probe the nature of the
compact object and its surroundings. In this talk, I shall give a
broad overview of the existing theoretical models for broadband
variability and different types of QPOs, with a focus on the findings
from the current state-of-art simulations of accretion discs in
reproducing such time variability phenomena. In particular, I will
discuss how the mass accretion rate fluctuations generated by the
turbulence in the simulations naturally explain the observed
broad-band variability in BHXRBs, and how the precession frequency of
the inner geometrically thick disc differs from the standard
Lense-Thirring precession frequency in truncated disc geometry and its
implications to Type-C QPOs.

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