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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

X-ray short-time lags in the Fe-K energy band produced by scattering clouds in active galactic nuclei Thumbnail


Authors

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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