Open AccessConstraints on active galactic nucleus accretion disc viscosity derived from continuum variability
Author(s) -
Starling Rhaana L. C.,
Siemiginowska Aneta,
Uttley Phil,
Soria Roberto
Publication year - 2004
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2004.07167.x
Subject(s) - physics , active galactic nucleus , accretion (finance) , astrophysics , quasar , magnetohydrodynamic drive , magnetohydrodynamics , viscosity , thermal , turbulence , accretion disc , astronomy , galaxy , magnetic field , mechanics , thermodynamics , quantum mechanics
We estimate a value of the viscosity parameter in active galactic nucleus (AGN) accretion discs for the Palomar–Green 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 α‐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, α. We obtain constraints of 0.01 ≤α≤ 0.03 for 0.01 ≤ L / L Edd ≤ 1.0 . This narrow range suggests that these AGNs are all seen in a single state, with a correspondingly narrow spread of black hole masses or accretion rates. The value of α we derive is consistent with predictions by current simulations in which magnetohydrodynamic (MHD) turbulence is the primary viscosity mechanism.