Accretion disc time lag distributions: applying CREAM to simulated AGN light curves

David Starkey*, Keith Horne, C. Villforth

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

30 Citations (Scopus)


Active galactic nuclei (AGN) vary in their brightness across all wavelengths. Moreover, longer wavelength ultraviolet-optical continuum light curves appear to be delayed with respect to shorter wavelength light curves. A simple way to model these delays is by assuming thermal reprocessing of a variable point source (a lamp post) by a blackbody accretion disc. We introduce a new method, CREAM (Continuum REprocessed AGN Markov Chain Monte Carlo), that models continuum variations using this lamp post model. The disc light curves lag the lamp post emission with a time delay distribution sensitive to the disc temperature-radius profile and inclination.We test CREAM's ability to recover both inclination and product of black hole mass and accretion rate MM˙ , and show that the code is also able to infer the shape of the driving light curve. CREAM is applied to synthetic light curves expected from 1000 s exposures of a 17th magnitude AGN with a 2-m telescope in Sloan g and i bands with Signal-to-Noise Ratio (SNR) of 500-900 depending on the filter and lunar phase.We also test CREAM on poorer quality g and i light curves with SNR = 100. We find in the high-SNR case that CREAM can recover the accretion disc inclination to within an uncertainty of 5° and an MM˙to within 0.04 dex.

Original languageEnglish
Pages (from-to)1960-1973
Number of pages14
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
Early online date30 Dec 2015
Publication statusPublished - 21 Feb 2016


  • Accretion, accretion discs
  • Methods: statistical
  • Quasars: supermassive black holes


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