Dr Misaki Mizumoto misaki.mizumoto@durham.ac.uk
Sponsored Researcher Post
X-ray short-time lags in the Fe-K energy band produced by scattering clouds in active galactic nuclei
Mizumoto, Misaki; Done, Chris; Hagino, Kouichi; Ebisawa, Ken; Tsujimoto, Masahiro; Odaka, Hirokazu
Authors
Professor Christine Done chris.done@durham.ac.uk
Professor
Kouichi Hagino
Ken Ebisawa
Masahiro Tsujimoto
Hirokazu Odaka
Abstract
X-rays illuminating the accretion disc in active galactic nuclei give rise to an iron K line and its associated reflection spectrum which are lagged behind the continuum variability by the light-travel time from the source to the disc. The measured lag timescales in the iron band can be as short as ∼Rg/c, where Rg is the gravitational radius, which is often interpreted as evidence for a very small continuum source close to the event horizon of a rapidly spinning black hole. However, the short lags can also be produced by reflection from more distant material, because the primary photons with no time-delay dilute the time-lags caused by the reprocessed photons. We perform a Monte-Carlo simulation to calculate the dilution effect in the X-ray reverberation lags from a half-shell of neutral material placed at 100 Rg from the central source. This gives lags of ∼2 Rg/c, but the iron line is a distinctly narrow feature in the lag-energy plot, whereas the data often show a broader line. We show that both the short lag and the line broadening can be reproduced if the scattering material is outflowing at ∼0.1c. The velocity structure in the wind can also give shifts in the line profile in the lag-energy plot calculated at different frequencies. Hence we propose that the observed broad iron reverberation lags and shifts in profile as a function of frequency of variability can arise from a disc wind at fairly large distances from the X-ray source.
Citation
Mizumoto, M., Done, C., Hagino, K., Ebisawa, K., Tsujimoto, M., & Odaka, H. (2018). X-ray short-time lags in the Fe-K energy band produced by scattering clouds in active galactic nuclei. Monthly Notices of the Royal Astronomical Society, 478(1), 971-982. https://doi.org/10.1093/mnras/sty1114
Journal Article Type | Article |
---|---|
Acceptance Date | Apr 27, 2018 |
Online Publication Date | May 2, 2018 |
Publication Date | Jul 21, 2018 |
Deposit Date | May 10, 2018 |
Publicly Available Date | Mar 29, 2024 |
Journal | Monthly Notices of the Royal Astronomical Society |
Print ISSN | 0035-8711 |
Electronic ISSN | 1365-2966 |
Publisher | Royal Astronomical Society |
Peer Reviewed | Peer Reviewed |
Volume | 478 |
Issue | 1 |
Pages | 971-982 |
DOI | https://doi.org/10.1093/mnras/sty1114 |
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Copyright Statement
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society © 2018 The Authors.
Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
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