ASTRO-H White Paper - AGN Reflection

TL;DR

This paper discusses how ASTRO-H X-ray observatory will enhance understanding of AGN central engines by analyzing reflection signatures, including iron lines and continuum features, to reveal the structure and dynamics of accretion disks and tori.

Contribution

It outlines the potential of ASTRO-H's high-resolution spectroscopy and broad-band observations to probe AGN reflection features, advancing models of black hole accretion and evolution.

Findings

High-resolution iron line spectroscopy will reveal torus dynamics and geometry.

Broad-band observations will constrain the shape of the X-ray continuum and reflection.

Detection of reverberation delays will provide insights into inner disk structure.

Abstract

X-ray observations provide a powerful tool to probe the central engines of active galactic nuclei (AGN). A hard X-ray continuum is produced from deep within the accretion flow onto the supermassive black hole, and all optically thick structures in the AGN (the dusty torus of AGN unification schemes, broad emission line clouds, and the black hole accretion disk) "light up" in response to irradiation by this continuum. This White Paper describes the prospects for probing AGN physics using observations of these X-ray reflection signatures. High-resolution SXS spectroscopy of the resulting fluorescent iron line in type-2 AGN will give us an unprecedented view of the obscuring torus, allowing us to assess its dynamics (through line broadening) and geometry (through the line profile as well as observations of the "Compton shoulder"). The broad-band view obtained by combining all of the ASTRO-H instruments will fully characterize the shape of the underlying continuum (which may be heavily absorbed) and reflection/scattering, providing crucial constraints on models for the Cosmic X-ray Background with a subsequent impact on understanding of supermassive black hole evolution. ASTRO-H will also permit the relativistically broadened reflection spectrum from the inner accretion disk to be robustly studied, even in complex systems with, for example, warm absorption and composite soft excesses. Finally, the HXI will allow the detection and study of reverberation delays between the continuum and the Compton reflection hump from the inner disk.