Constraints on AGN accretion disc viscosity derived from continuum variability
Abstract
We estimate a value of the viscosity parameter in AGN accretion discs for the PG quasar sample. We assume that optical variability on time-scales of months to years is caused by local instabilities in the inner accretion disc. Comparing the observed variability time-scales to the thermal time-scales of alpha-disc models we obtain constraints on the viscosity parameter for the sample. We find that, at a given L/L_Edd, the entire sample is consistent with a single value of the viscosity parameter, alpha. We obtain constraints of 0.01 < alpha < 0.03 for 0.01 < L/L_Edd < 1.0. This narrow range suggests that these AGN are all seen in a single state, with a correspondingly narrow spread of black hole masses or accretion rates. The value of alpha we derive is consistent with predictions by current simulation s in which MHD turbulence is the primary viscosity mechanism.
Keywords
Cite
@article{arxiv.astro-ph/0309291,
title = {Constraints on AGN accretion disc viscosity derived from continuum variability},
author = {Rhaana L. C. Starling and Aneta Siemiginowska and Phil Uttley and Roberto Soria},
journal= {arXiv preprint arXiv:astro-ph/0309291},
year = {2009}
}
Comments
7 pages, 5 figures. Accepted for publication in Monthly Notices of the Royal Astronomical Society