Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Constraints on the Viscosity and Magnetic Field in Hot Accretion Flows
  around Black Holes   The magnitude of the viscosity and magnetic field parameters in hot accretion
flows is investigated in low luminosity active galactic nuclei (LLAGNs).
Theoretical studies show that a geometrically thin, optically thick disk is
truncated at mass accretion rates less than a critical value by mass evaporated
vertically from the disk to the corona, with the truncated region replaced by
an advection dominated accretion flow (ADAF). The critical accretion rate for
such a truncation is a function of the viscosity and magnetic field.
Observations of X-ray photon indices and spectral fits of a number of LLAGNs
published in the literature provide an estimate of the critical rate of mass
accretion and the truncation radius respectively. By comparing the
observational results with theoretical predictions, the viscosity and magnetic
field parameters in the hot accretion flow region are estimated. Specifically,
the mass accretion rates inferred in different sources constrain the viscosity
parameter, whereas the truncation radii of the disk, as inferred from spectral
fits, further constrain the magnetic field parameter. It is found that the
value of the viscosity parameter in the corona/ADAF ranges from 0.17 to 0.5,
with values clustered about 0.2-0.3. Magnetic pressure is required by the
relatively small truncation radii for some LLAGNs and is found to be as high as
its equipartition value with the gas pressure. The inferred values of the
viscosity parameter are in agreement with those obtained from the observations
of non-stationary accretion in stellar mass black hole X-ray transients. This
consistency provides support for the paradigm that a geometrically thin disk is
truncated by means of a mass evaporation process from the disk to the corona at
low mass accretion rates.

24
The categories of this paper are: dg-ga
14
The categories of this paper are: math-ph
22
The categories of this paper are: chao-dyn
4
The categories of this paper are: cond-mat
36
The categories of this paper are: cmp-lg
37
The categories of this paper are: supr-con
17
The categories of this paper are: q-fin
20
The categories of this paper are: acc-phys
1
The categories of this paper are: cs
28
The categories of this paper are: alg-geom
12
The categories of this paper are: nucl-th
9
The categories of this paper are: nlin
2
The categories of this paper are: math
25
The categories of this paper are: patt-sol
7
The categories of this paper are: hep-th
35
The categories of this paper are: mtrl-th