2 research outputs found
Accretion flows: the Role of the Outer Boundary Condition
We investigate the influences of the outer boundary conditions(OBCs) on the
structure of an optically thin accretion flow. We find that OBC plays an
important role in determining the topological structure and the profiles of the
surface density and temperature of the solution, therefore it should be
regarded as a new parameter in the accretion disk model.Comment: 9 pages, 2 figures, to appear in ApJ Letters, Vol. 521, L5
The role of the outer boundary condition in accretion disk models: theory and application
The influence of the outer boundary condition (OBC) on the dynamics and
radiation of optically thin accretion flow is investigated. Bremsstrahlung and
synchrotron radiations amplified by Comptonization are taken into account and
two-temperature plasma assumption is adopted. The three OBCs we adopted are the
temperatures of the electrons and ions and the specific angular momentum of the
accretion flow at a certain outer boundary. We find that when the general
parameters such as the mass accretion rate and the viscous parameter are fixed,
the peak flux at various bands such as radio, IR and X-ray, can differ by as
large as several orders of magnitude under different OBCs in our example. Our
results indicate that OBC is both dynamically and radiatively important
therefore should be regarded as a new ``parameter'' in accretion disk models.
We apply the above results to the compact radio source Sgr A* and find that the
discrepancy between the mass accretion rate favored by ADAF models in the
literature and that favored by the three dimensional hydrodynamical simulation
can be naturally resolved by seriously considering the outer boundary condition
of the accretion flow.Comment: 23 pages, 9 figures,accepted by the Astrophysical Journa