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dc.contributor.authorWeaver, J
dc.contributor.authorHorne, Keith Douglas
dc.identifier.citationWeaver , J & Horne , K D 2022 , ' Dust and the intrinsic spectral index of quasar variations : hints of finite stress at the innermost stable circular orbit ' , Monthly Notices of the Royal Astronomical Society , vol. 512 , no. 1 , pp. 899-916 .
dc.identifier.otherPURE: 277604028
dc.identifier.otherPURE UUID: f9f0f1ef-6d22-4906-91b6-fbf359e5473e
dc.identifier.otherWOS: 000770401200003
dc.identifier.otherScopus: 85127972928
dc.descriptionFunding: The Cosmic Dawn Center (DAWN) is funded by the Danish National Research Foundation under grant No. 140. J.W. acknowledges support from the European Research Council (ERC) Consolidator Grant funding scheme (project ConTExt, grant No. 648179), and from the University of St Andrews Undergraduate Research Assistant Scheme. K.H. acknowledges support from STFC grant ST/R000824/1.en
dc.description.abstractWe present a study of 9242 spectroscopically-confirmed quasars with multi-epoch ugriz photometry from the SDSS Southern Survey. By fitting a separable linear model to each quasar's spectral variations, we decompose their five-band spectral energy distributions into variable (disc) and non-variable (host galaxy) components. In modelling the disc spectra, we include attenuation by dust on the line of sight through the host galaxy to its nucleus. We consider five commonly used attenuation laws, and find that the best description is by dust similar to that of the Small Magellanic Cloud, inferring a lack of carbonaceous grains from the relatively weak 2175 Å absorption feature. We go on to construct a composite spectrum for the quasar variations spanning 700 to 8000 Å. By varying the assumed power-law Lv ∝ va spectral slope, we find a best-fit value = 0:71 ±  0:02, excluding at high confidence the canonical Lv ∝ v1/3 prediction for a steady-state accretion disc with a T ∝ r-3/4 temperature profile. The bluer spectral index of the observed quasar variations instead supports the model of Mummery & Balbus in which a steeper temperature profile, T ∝ r-7/8, develops as a result of finite magnetically-induced stress at the innermost stable circular orbit extracting energy and angular momentum from the black hole spin.
dc.relation.ispartofMonthly Notices of the Royal Astronomical Societyen
dc.rightsCopyright © 2022 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.en
dc.subjectAccretion discsen
dc.subjectQuasars: supermassive black holesen
dc.subjectMethods: statisticalen
dc.subjectQB Astronomyen
dc.subjectQC Physicsen
dc.titleDust and the intrinsic spectral index of quasar variations : hints of finite stress at the innermost stable circular orbiten
dc.typeJournal articleen
dc.contributor.sponsorScience & Technology Facilities Councilen
dc.description.versionPublisher PDFen
dc.contributor.institutionUniversity of St Andrews. St Andrews Centre for Exoplanet Scienceen
dc.contributor.institutionUniversity of St Andrews. School of Physics and Astronomyen
dc.description.statusPeer revieweden

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