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A physical model for the X-ray time lags of narrow-line Seyfert type 1 active galactic nuclei

Gardner, E.; Done, C.

A physical model for the X-ray time lags of narrow-line Seyfert type 1 active galactic nuclei Thumbnail


Authors

E. Gardner



Abstract

We study the origin of the soft X-ray excess seen in the ‘simple’ narrow-line Seyfert 1 galaxy PG1244+026 using all available spectral-timing information. This object shows the now ubiquitous switch between soft leading the hard band on long time-scales, to the opposite behaviour on short time-scales. This is interpreted as a combination of intrinsic fluctuations propagating down through the accretion flow giving the soft lead, together with reflection of the hard X-rays giving the soft lag. We build a full model of the spectral and time variability including both propagation and reflection, and compare our model with the observed power spectra, coherence, covariance, lag-frequency and lag-energy spectra. We compare models based on a separate soft excess component with those based on reflection-dominated soft emission. Reflection-dominated spectra have difficulty reproducing the soft lead at low frequency since reflection will always lag. They also suffer from high coherence and nearly identical hard- and soft-band power spectra in disagreement with the observations. This is a direct result of the power-law and reflection components both contributing to the hard and soft energy bands, and the small radii over which the relativistically smeared reflection is produced allowing too much high-frequency power to be transmitted into the soft band. Conversely, we find the separate soft excess models (where the inner disc radius is >6Rg) have difficulty reproducing the soft lag at high frequency, as reflected flux does not contribute enough signal to overwhelm the soft lead. However, reflection should also be accompanied by reprocessing and this should add to the soft excess at low energies. This model can quantitatively reproduce the switch from soft lead to soft lag seen in the data and reproduces well the observed power spectra and other timing features which reflection-dominated models cannot.

Citation

Gardner, E., & Done, C. (2014). A physical model for the X-ray time lags of narrow-line Seyfert type 1 active galactic nuclei. Monthly Notices of the Royal Astronomical Society, 442(3), 2456-2473. https://doi.org/10.1093/mnras/stu1026

Journal Article Type Article
Acceptance Date May 21, 2014
Online Publication Date Jun 24, 2014
Publication Date Aug 11, 2014
Deposit Date Mar 16, 2016
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 442
Issue 3
Pages 2456-2473
DOI https://doi.org/10.1093/mnras/stu1026
Related Public URLs http://adsabs.harvard.edu/abs/2014MNRAS.442.2456G

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Copyright Statement
This article has been accepted for publication in Monthly notices of the Royal Astronomical Society ©: 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.





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