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Accurate Treatment of Comptonization in X-ray Illuminated Accretion Disks

García, Javier A. and Sokolova-Lapa, Ekaterina and Dauser, Thomas and Madej, Jerzy and Różańska, Agata and Majczyna, Agnieszka and Harrison, Fiona A. and Wilms, Jörn (2020) Accurate Treatment of Comptonization in X-ray Illuminated Accretion Disks. Astrophysical Journal, 897 (1). Art. No. 67. ISSN 1538-4357. doi:10.3847/1538-4357/ab919b.

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A large fraction of accreting black hole and neutron star systems present clear evidence of the reprocessing of X-rays in the atmosphere of an optically thick accretion disk. The main hallmarks of X-ray reflection include fluorescent K-shell emission lines from iron (~6.4–6.9 keV), the absorption iron K-edge (~7–9 keV), and a broad featureless component known as the Compton hump (~20–40 keV). This Compton hump is produced as the result of the scattering of high-energy photons (E ≳ 10 keV) of the relatively colder electrons (T_e ~ 10⁵–10⁷ K) in the accretion disk, in combination with photoelectric absorption from iron. The treatment of this process in most current models of ionized X-ray reflection has been done using an approximated Gaussian redistribution kernel. This approach works sufficiently well up to ~100 keV, but it becomes largely inaccurate at higher energies and at relativistic temperatures (T_e ~ 10⁹ K). We present new calculations of X-ray reflection using a modified version of our code xillver, including an accurate solution for Compton scattering of the reflected unpolarized photons in the disk atmosphere. This solution takes into account quantum electrodynamic and relativistic effects allowing the correct treatment of high photon energies and electron temperatures. We show new reflection spectra computed with this model, and discuss the improvements achieved in reproducing the correct shape of the Compton hump, the discrepancies with previous calculations, and the expected impact of these new models in the interpretation of observational data.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
García, Javier A.0000-0003-3828-2448
Dauser, Thomas0000-0003-4583-9048
Madej, Jerzy0000-0001-8417-1509
Różańska, Agata0000-0002-5275-4096
Harrison, Fiona A.0000-0003-2992-8024
Wilms, Jörn0000-0003-2065-5410
Additional Information:© 2020 The American Astronomical Society. Received 2020 March 14; revised 2020 May 7; accepted 2020 May 8; published 2020 July 2. This work was been partially supported under NASA No. NNG08FD60C. J.A.G. acknowledges support from NASA ATP grant No. 80NSSC20K0540 and from the Alexander von Humboldt Foundation. E.K.S and J.W. have been supported by DFG grant WI 1860/11-1. A.R., J.M., and A.M. were supported by grants No. 2015/17/B/ST9/03422 and 2015/18/M/ST9/00541 from the Polish National Science Center. software xillver (García & Kallman 2010; García et al. 2013), Matplotlib (version 3.1.3, Hunter 2007), NumPy (version 1.18.1, Oliphant 2006).
Group:Astronomy Department, Space Radiation Laboratory
Funding AgencyGrant Number
Alexander von Humboldt FoundationUNSPECIFIED
Deutsche Forschungsgemeinschaft (DFG)WI 1860/11-1
National Science Centre (Poland)2015/17/B/ST9/03422
National Science Centre (Poland)2015/18/M/ST9/00541
Subject Keywords:Accretion ; Stellar accretion disks ; Atomic spectroscopy ; Radiative transfer simulations ; Astronomical simulations ; Black hole physics
Issue or Number:1
Classification Code:Unified Astronomy Thesaurus concepts: Accretion (14); Stellar accretion disks (1579); Atomic spectroscopy (2099); Radiative transfer simulations (1967); Astronomical simulations (1857); Black hole physics (159)
Record Number:CaltechAUTHORS:20200604-151447853
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Official Citation:Javier A. García et al 2020 ApJ 897 67
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:103713
Deposited By: George Porter
Deposited On:05 Jun 2020 14:30
Last Modified:16 Nov 2021 18:24

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