Fourier spectral-timing techniques for the study of accreting black holes

TL;DR

This paper reviews spectral-timing techniques used to study the innermost regions of accreting black holes, highlighting methods like reverberation mapping and phase-resolved spectroscopy that reveal black hole properties and QPO mechanisms.

Contribution

It provides a concise overview of spectral-timing methods, emphasizing their application to black hole accretion studies and the insights gained into black hole geometry and QPOs.

Findings

Reverberation mapping diagnoses accretion geometry and black hole mass.

Phase-resolved spectroscopy constrains low frequency QPO mechanisms.

Spectral-timing techniques offer causal insights into black hole environments.

Abstract

The X-ray signal from active galactic nuclei and black hole X-ray binaries is highly variable on a range of timescales. This variability can be exploited to map the region of interest close to the black hole, which is far too small to directly image for all but two black holes in the Universe. Spectral-timing techniques provide causal information by combining timing and spectral information. I present a brief review of such techniques, focusing on two examples: X-ray reverberation mapping and phase-resolved spectroscopy of low frequency quasi-periodic oscillations (LF QPOs). The former provides a means to diagnose the accretion geometry and measure parameters such as black hole mass, and the latter gives perhaps the best constraints we currently have as to the enigmatic LF QPO mechanism.