Investigating the Impact of Vertically Extended Coronae on X-Ray Reverberation Mapping
Accreting black holes commonly exhibit hard X-ray emission, originating from a region of hot plasma near the central engine referred to as the corona. The origin and geometry of the corona are poorly understood, and models invoking either inflowing or outflowing material (or both) can successfully explain only parts of the observed phenomenology. In particular, recent works indicate that the time-averaged and variability property might originate in different regions of the corona. In this paper we present a model designed to move beyond the lamppost paradigm, with the goal of accounting for the vertical extent of the corona. In particular, we highlight the impact of including self-consistently a second lamppost, mimicking, for example, an extended jet base. We fully include the effect that the second source has on the time-dependent disk ionization, reflection spectrum, and reverberation lags. We also present an application of this new model to NICER observations of the X-ray binary MAXI J1820+070 near its hard-to-soft state transition. We demonstrate that in these observations, a vertically extended corona can capture both spectral and timing properties, while a single-lamppost model can not. In this scenario, the illumination responsible for the time-averaged spectrum originates close to the black hole, while the variability is likely associated with the ballistic jet.
Additional Information© 2023. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. We thank the anonymous referee for insightful comments, which have improved the manuscript. M.L., G.M., J.W., E.K., and J.A.G. acknowledge support from NASA ADAP grant 80NSSC17K0515. J.W. acknowledges support from the NASA FINNEST Graduate Fellowship, under grant 80NSSC22K1596. A.I. acknowledges support from the Royal Society. M.K. acknowledges support from the NWO Spinoza Prize. O.K. acknowledges funding by the Deutsches Zentrum für Luft- und Raumfahrt, contract 50 QR 2103. This research has made use of ISIS functions (ISISscripts) provided by ECAP/Remeis observatory and MIT (http://www.sternwarte.uni-erlangen.de/isis/). Software: Heasoft (Nasa High Energy Astrophysics Science Archive Research Center (Heasarc), 2014)), XSPEC (Arnaud 1996), ISIS (Houck & Denicola 2000), Reltrans (Ingram et al. 2019), Numpy (Harris et al. 2020), Matplotlib (Hunter 2007).
Published - Lucchini_2023_ApJ_951_19.pdf