Testing super-eddington accretion on to a supermassive black hole: reverberation mapping of PG 1119+120

Fergus R Donnan*, Juan V. Hernandez Santisteban, Keith Horne, Chen Hu, Pu Du, Yan-Rong Li, Ming Xiao, Luis C Ho, Jesús Aceituno, Jian-Min Wang, Wei-Jian Guo, Sen Yang, Bo-Wei Jiang, Zhu-Heng Yao

*Corresponding author for this work

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Abstract

We measure the black hole mass and investigate the accretion flow around the local (z = 0.0502) quasar PG 1119+120. Spectroscopic monitoring with Calar Alto provides H β lags and linewidths from which we estimate a black hole mass of log (M•/M⊙) = 7.0, uncertain by ∼0.4 dex. High cadence photometric monitoring over 2 yr with the Las Cumbres Observatory provides light curves in seven optical bands suitable for intensive continuum reverberation mapping. We identify variability on two time-scales. Slower variations on a 100-d time-scale exhibit excess flux and increased lag in the u′ band and are thus attributable to diffuse bound-free continuum emission from the broad-line region. Faster variations that we attribute to accretion disc reprocessing lack a u′-band excess and have flux and delay spectra consistent with either τ ∝ λ4/3, as expected for a temperature structure of T(R) ∝ R−3/4 for a thin accretion disc, or τ ∝ λ2 expected for a slim disc. Decomposing the flux into variable (disc) and constant (host galaxy) components, we find the disc SED to be flatter than expected with ƒv ∼ const. Modelling the SED predicts an Eddington ratio of λEdd > 1, where the flat spectrum can be reproduced by a slim disc with little dust extinction or a thin disc that requires more dust extinction. While this accretion is super-Eddington, the geometry is still unclear; however, a slim disc is expected due to the high radiation pressure at these accretion rates, and is entirely consistent with our observations.
Original languageEnglish
Pages (from-to)545-567
Number of pages23
JournalMonthly Notices of the Royal Astronomical Society
Volume523
Issue number1
Early online date25 May 2023
DOIs
Publication statusPublished - 1 Jul 2023

Keywords

  • Accretion
  • Accretion discs
  • Galaxies: inactive
  • Galaxies: individual: PG1119+120

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