ESTIMATION OF THE VISCOSITY PARAMETER IN ACCRETION DISKS OF BLAZARS
- Physics Department, Yunnan Normal University, Kunming 650092 (China)
For an optical monitoring blazar sample set whose typical minimum variability timescale is about 1 hr, we estimate a mean value of the viscosity parameter in their accretion disk. We assume that optical variability on timescales of hours is caused by local instabilities in the inner accretion disk. Comparing the observed variability timescales to the thermal timescales of alpha-disk models, we could obtain constraints on the viscosity parameter (alpha) and the intrinsic Eddington ratio (L{sup in}/L{sub Edd}=m-dot), 0.104 <= alpha <= 0.337, and 0.0201 <= L {sup in}/L{sub Edd} <= 0.1646. These narrow ranges suggest that all these blazars are observed in a single state, and thus provide a new evidence for the unification of flat-spectrum radio quasars and BL Lacs into a single blazar population. The values of alpha we derive are consistent with the theoretical expectation alpha approx 0.1-0.3 of Narayan and Mcclintock for advection-dominated accretion flow and are also compatible with Pessah et al.'s predictions (alpha >= 0.1) by numerical simulations in which magnetohydrodynamic turbulence is driven by the saturated magnetorotational instability.
- OSTI ID:
- 21392591
- Journal Information:
- Astrophysical Journal, Vol. 707, Issue 2; Other Information: DOI: 10.1088/0004-637X/707/2/866; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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