Accretion disc time lag distributions : applying CREAM to simulated AGN light curves
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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.
Starkey , D , Horne , K & Villforth , C 2016 , ' Accretion disc time lag distributions : applying CREAM to simulated AGN light curves ' Monthly Notices of the Royal Astronomical Society , vol 456 , no. 2 , pp. 1960-1973 . DOI: 10.1093/mnras/stv2744
Monthly Notices of the Royal Astronomical Society
© 2015 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. This work is made available online in accordance with the publisher’s policies. This is the final published version of the work, which was originally published at https://dx.doi.org/10.1093/mnras/stv2744
DAS acknowledges the support of the Science and Technologies Funding Council studentship. KH acknowledges support from the UK Science and Technology Facilities Council (STFC) consolidated grant to St Andrews (ST/M001296/1).
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