Skip to main content

Research Repository

Advanced Search

Discarding the disc in a changing-state AGN: the UV/X-ray relation in NGC 4151

Mahmoud, Ra'ad D.; Done, Chris

Discarding the disc in a changing-state AGN: the UV/X-ray relation in NGC 4151 Thumbnail


Authors

Ra'ad D. Mahmoud



Abstract

Recent monitoring campaigns designed to map the accretion regime in AGN show major discrepancies with models where the optical/ultraviolet (UV) is produced by X-ray-illuminated, optically thick disc material within a few hundred gravitational radii. However, these campaigns only monitored X-rays below 10 keV, whereas the bolometric luminosity for most of these AGN peaks above 50 keV. We use data from the recent multiwavelength campaign by Edelson et al. (2017) on NGC 4151 - the only AGN bright enough to be monitored at higher energies with Swift BAT. We develop a spectral-timing model with a hot corona, warm Comptonisation, and outer standard disc. This fits the time-averaged spectrum well, but completely fails to match the UV variability predicted from the X-ray lightcurve. However, it reveals that NGC 4151 had a bolometric luminosity around 1.4% of the Eddington luminosity during this campaign, close to the luminosity at which AGN show a ‘changing-state’ transition, where the broad optical lines disappear. Stellar mass black holes show a state transition at a similarly low Eddington fraction, which is broadly interpreted as the inner disc being replaced by an optically thin flow. We find that the UV lightcurve can instead be matched by reprocessing of the X-ray flux on size scales of the broad line region (BLR; 1.5 − 20 light-days) and rule out there being optically thick material inwards of this, as expected if the thin disc is replaced by the flow below the inner radius of the BLR. These results emphasise the need for even longer-timescale, multiwavelength monitoring campaigns on variable AGN.

Citation

Mahmoud, R. D., & Done, C. (2020). Discarding the disc in a changing-state AGN: the UV/X-ray relation in NGC 4151. Monthly Notices of the Royal Astronomical Society, 491(4), 5126-5139. https://doi.org/10.1093/mnras/stz3196

Journal Article Type Article
Acceptance Date Nov 12, 2019
Online Publication Date Nov 15, 2019
Publication Date 2020-02
Deposit Date Nov 14, 2019
Publicly Available Date Mar 28, 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 491
Issue 4
Pages 5126-5139
DOI https://doi.org/10.1093/mnras/stz3196

Files

Accepted Journal Article (2.4 Mb)
PDF

Copyright Statement
This article has been accepted for publication in the Monthly notices of the Royal Astronomical Society ©: 2019 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.






You might also like



Downloadable Citations