Swift monitoring observations of Mrk 231: detection of ultraviolet variability
Swift monitoring observations of Mrk 231: detection of ultraviolet variability
We analyse 168 Swift monitoring observations of the nearest broad absorption line quasar Mrk 231 in the ultraviolet (UV) and X-ray bands, where we detect significant variability in the UV (~2246 Å) light curve with a null probability of 4.3 × 10-10 for a constant model. Separately, from an archival sample of Swift observed active galactic nuclei (AGNs), we measure the relation between UV excess variance and luminosity, finding that the normalized UVexcess variance decreases with luminosity. Comparing to thismean relation, the normalized UV excess variance of Mrk 231 is smaller, however within the scatter characterizing the full population. The upper limit of the X-ray excess variance is consistent with other AGN. The power spectrum density (PSD) of the UV light curve can be well fit by a power-law model with a slope of 1.82 ± 0.14 between 10-7.5 and 10-6 Hz, consistent with those for typical AGN, with no obvious quasi-periodical oscillation peaks. The UV variability and its power spectrum suggest that a significant amount of theUVemission of Mrk 231 is from the accretion disc. The consistencies in the normalized UV variability and the shape of the PSD between Mrk 231 and other normal AGN suggest that the origin of UV variability of broad absorption line quasars is similar to other AGN, and dust scattering at large scales such as the torus is not a dominating process for the UV emission of Mrk 231. Significant scattering, if present, is constrained to smaller than ~10 light days. We perform lagged correlation analysis between the UV and X-ray light curves and find the correlation insignificant within the present data.
Accretion, accretion discs, Black hole physics, Galaxies: active, Galaxies: individual (Mrk 231), Quasars: absorption lines, Ultraviolet: general
5504-5510
Yang, Lilan
74da557a-ab37-42b0-95d1-d55a6d8812bf
Dai, Xinyu
c76ef1e8-85d4-4c25-890d-6cba7f08627e
Lu, Youjun
3cfd6ee7-2257-4185-9c37-c1df34e1f35e
Zhu1, Zong Hong
ef88c40e-31b5-4e4c-b1d2-b339aebeca0d
Shankar, Francesco
b10c91e4-85cd-4394-a18a-d4f049fd9cdb
11 November 2018
Yang, Lilan
74da557a-ab37-42b0-95d1-d55a6d8812bf
Dai, Xinyu
c76ef1e8-85d4-4c25-890d-6cba7f08627e
Lu, Youjun
3cfd6ee7-2257-4185-9c37-c1df34e1f35e
Zhu1, Zong Hong
ef88c40e-31b5-4e4c-b1d2-b339aebeca0d
Shankar, Francesco
b10c91e4-85cd-4394-a18a-d4f049fd9cdb
Yang, Lilan, Dai, Xinyu, Lu, Youjun, Zhu1, Zong Hong and Shankar, Francesco
(2018)
Swift monitoring observations of Mrk 231: detection of ultraviolet variability.
Monthly Notices of the Royal Astronomical Society, 480 (4), .
(doi:10.1093/MNRAS/STY2253).
Abstract
We analyse 168 Swift monitoring observations of the nearest broad absorption line quasar Mrk 231 in the ultraviolet (UV) and X-ray bands, where we detect significant variability in the UV (~2246 Å) light curve with a null probability of 4.3 × 10-10 for a constant model. Separately, from an archival sample of Swift observed active galactic nuclei (AGNs), we measure the relation between UV excess variance and luminosity, finding that the normalized UVexcess variance decreases with luminosity. Comparing to thismean relation, the normalized UV excess variance of Mrk 231 is smaller, however within the scatter characterizing the full population. The upper limit of the X-ray excess variance is consistent with other AGN. The power spectrum density (PSD) of the UV light curve can be well fit by a power-law model with a slope of 1.82 ± 0.14 between 10-7.5 and 10-6 Hz, consistent with those for typical AGN, with no obvious quasi-periodical oscillation peaks. The UV variability and its power spectrum suggest that a significant amount of theUVemission of Mrk 231 is from the accretion disc. The consistencies in the normalized UV variability and the shape of the PSD between Mrk 231 and other normal AGN suggest that the origin of UV variability of broad absorption line quasars is similar to other AGN, and dust scattering at large scales such as the torus is not a dominating process for the UV emission of Mrk 231. Significant scattering, if present, is constrained to smaller than ~10 light days. We perform lagged correlation analysis between the UV and X-ray light curves and find the correlation insignificant within the present data.
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Accepted/In Press date: 14 August 2018
e-pub ahead of print date: 18 August 2018
Published date: 11 November 2018
Additional Information:
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.
Keywords:
Accretion, accretion discs, Black hole physics, Galaxies: active, Galaxies: individual (Mrk 231), Quasars: absorption lines, Ultraviolet: general
Identifiers
Local EPrints ID: 426082
URI: http://eprints.soton.ac.uk/id/eprint/426082
ISSN: 1365-2966
PURE UUID: 9453c522-f490-4db6-8a84-1320b0f65b4e
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Date deposited: 13 Nov 2018 17:30
Last modified: 09 Apr 2025 18:27
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Contributors
Author:
Lilan Yang
Author:
Xinyu Dai
Author:
Youjun Lu
Author:
Zong Hong Zhu1
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