The effect of returning radiation on relativistic reflection
We study the effect of returning radiation on the shape of the X-ray reflection spectrum in the case of thin accretion discs. We show that the returning radiation mainly influences the observed reflection spectrum for a large black hole spin (a > 0.9) and a compact primary source of radiation close to the black hole at height h < 5r_g, and that it dominates the reflected flux for extreme values of spin and compactness. The main effect of the returning radiation is to increase the irradiating flux on to the outer parts of the accretion disc, leading to stronger reflection and a flatter overall emissivity profile. By analysing simulated observations we show that neglecting returning radiation in existing studies of reflection-dominated sources has likely resulted in overestimating the height of the corona above the black hole. An updated version of the publicly available relxill suite of relativistic reflection models which includes returning radiation is also presented.
© 2022 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model). Received: 08 June 2021. Revision received: 02 June 2022. Accepted: 06 June 2022. Published: 15 June 2022. We would like to express sincere thanks to the anonymous referee with whom we had a comprehensive and illuminating discourse which allowed us to improve the clarity and veracity of our paper to the current state. TD acknowledges funding by the Deutsches Zentrum für Luft- und Raumfahrt contract 50 QR 1903. AI acknowledges support from the Royal Society. AJ acknowledges partial funding from the European Space Agency (ESA) under partnership agreement 4000133194/20/NL/MH/hm between ESA and FAU Erlangen-Nürnberg. JAG acknowledges support from an Alexander von Humboldt fellowship. We thank John E. Davis for the development of the SLXFIG module used to prepare the figures in this paper. This research has made use of ISIS functions provided by ECAP/Remeis observatory and MIT (http://www.sternwarte.uni-erlangen.de/isis/). DATA AVAILABILITY. The data underlying this article will be shared on reasonable request to the corresponding author.
Accepted Version - 2206.07973.pdf
Published - stac1593.pdf