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Modelling correlated variability in accreting black holes: the effect of high density and variable ionization on reverberation lags

Mastroserio, Guglielmo and Ingram, Adam and Wang, Jingyi and García, Javier A. and van der Klis, Michiel and Cavecchi, Yuri and Connors, Riley and Dauser, Thomas and Harrison, Fiona and Kara, Erin and König, Ole and Lucchini, Matteo (2021) Modelling correlated variability in accreting black holes: the effect of high density and variable ionization on reverberation lags. Monthly Notices of the Royal Astronomical Society, 507 (1). pp. 55-73. ISSN 0035-8711. doi:10.1093/mnras/stab2056.

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We present a new release of the RELTRANS model to fit the complex cross-spectrum of accreting black holes as a function of energy. The model accounts for continuum lags and reverberation lags self-consistently in order to consider the widest possible range of X-ray variability time-scales. We introduce a more self-consistent treatment of the reverberation lags, accounting for how the time variations of the illuminating flux change the ionization level of the accretion disc. This process varies the shape of the reflection spectrum in time causing an additional source of lags besides the light crossing delay. We also consider electron densities in the accretion disc up to 10²⁰ cm⁻³, which are found in most of the stellar mass black holes and in some active galactic nuclei. These high densities increase the amplitude of the reverberation lags below 1 keV since the reflection flux enhances in the same energy range. In addition, we investigate the properties of hard lags produced by variations in the power-law index of the continuum spectrum, which can be interpreted as due to roughly 3 per cent3 per cent variability in the corona’s optical depth and temperature. As a test case, we simultaneously fit the lag-energy spectra in a wide range of Fourier frequency for the black hole candidate MAXI J1820+0701820 observed with NICER. The best fit shows how the reverberation lags contribute even at the longer time-scales where the hard lags are important. This proves the importance of modelling these two lags together and self-consistently in order to constrain the parameters of the system.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper ItemRELTRANS Model Package
Mastroserio, Guglielmo0000-0003-4216-7936
Ingram, Adam0000-0002-5311-9078
Wang, Jingyi0000-0002-1742-2125
García, Javier A.0000-0003-3828-2448
van der Klis, Michiel0000-0003-0070-9872
Cavecchi, Yuri0000-0002-6447-3603
Connors, Riley0000-0002-8908-759X
Dauser, Thomas0000-0003-4583-9048
Harrison, Fiona0000-0003-2992-8024
Kara, Erin0000-0003-0172-0854
Lucchini, Matteo0000-0002-2235-3347
Additional Information:© 2021 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 ( Accepted 2021 July 11. Received 2021 July 8; in original form 2021 March 12. Published: 21 July 2021. The authors would like to acknowledge the anonymous referee for the very helpful comments and suggestions. GM, JW, EK, and JAG acknowledge support from the NASA grant 80NSSC17K0515. AI acknowledges support from the Royal Society. MK thanks the support from NWO Spinoza. JAG thanks support from the Alexander von Humboldt Foundation. This work was partially supported under NASA contract No. NNG08FD60C. Data Availability: The source code for the model described in this paper will soon be made publicly available in the form of an update to the RELTRANS model package ( The NICER observation is publicly available at the HEASOFT webpage.
Group:Astronomy Department, Space Radiation Laboratory
Funding AgencyGrant Number
Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO)UNSPECIFIED
Alexander von Humboldt FoundationUNSPECIFIED
Subject Keywords:accretion, accretion discs – black hole physics – relativistic processes – X-rays: binaries – X-rays: galaxies
Issue or Number:1
Record Number:CaltechAUTHORS:20211020-164833304
Persistent URL:
Official Citation:Guglielmo Mastroserio, Adam Ingram, Jingyi Wang, Javier A García, Michiel van der Klis, Yuri Cavecchi, Riley Connors, Thomas Dauser, Fiona Harrison, Erin Kara, Ole König, Matteo Lucchini, Modelling correlated variability in accreting black holes: the effect of high density and variable ionization on reverberation lags, Monthly Notices of the Royal Astronomical Society, Volume 507, Issue 1, October 2021, Pages 55–73,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:111552
Deposited By: Tony Diaz
Deposited On:20 Oct 2021 22:33
Last Modified:21 Oct 2021 16:42

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