Skip to main content

Research Repository

Advanced Search

The broad-band SEDs of four ‘hypervariable’ AGN

Collinson, James S.; Ward, Martin J.; Lawrence, Andy; Bruce, Alastair; MacLeod, Chelsea L.; Elvis, Martin; Gezari, Suvi; Marshall, Philip J.; Done, Chris

The broad-band SEDs of four ‘hypervariable’ AGN Thumbnail


James S. Collinson

Andy Lawrence

Alastair Bruce

Chelsea L. MacLeod

Martin Elvis

Suvi Gezari

Philip J. Marshall

Chris Done


We present an optical-to-X-ray spectral analysis of four ‘hypervariable’ AGN (HVAs) discovered by comparing Pan-STARRS data to that from the Sloan Digital Sky Survey over a 10 yr baseline (Lawrence et al.). There is some evidence that these objects are X-ray loud for their corresponding UV luminosities, but given that we measured them in a historic high state, it is not clear whether to take the high state or low state as typical of the properties of these HVAs. We estimate black hole masses based on Mg II and H α emission line profiles, and either the high- or low-state luminosities, finding mass ranges log (MBH/M⊙) = 8.2–8.8 and log (MBH/M⊙) = 7.9–8.3, respectively. We then fit energy-conserving models to the spectral energy distributions (SEDs), obtaining strong constraints on the bolometric luminosity and αOX. We compare the SED properties with a larger, X-ray selected AGN sample for both of these scenarios, and observe distinct groupings in spectral shape versus luminosity parameter space. In general, the SED properties are closer to normal if we assume that the low state is representative. This supports the idea that the large slow outbursts may be due to extrinsic effects (for example microlensing) as opposed to accretion rate changes, but a larger sample of HVAs is needed to be confident of this conclusion.


Collinson, J. S., Ward, M. J., Lawrence, A., Bruce, A., MacLeod, C. L., Elvis, M., …Done, C. (2018). The broad-band SEDs of four ‘hypervariable’ AGN. Monthly Notices of the Royal Astronomical Society, 474(3), 3565-3575.

Journal Article Type Article
Acceptance Date Nov 17, 2017
Online Publication Date Nov 24, 2017
Publication Date Mar 1, 2018
Deposit Date Jan 18, 2018
Publicly Available Date Jan 18, 2018
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 474
Issue 3
Pages 3565-3575


Published Journal Article (2 Mb)

Copyright Statement
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2017 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

You might also like

Downloadable Citations