1112.0726 (Osamu Kaburaki)
Osamu Kaburaki
In a series of our previous works, a model of radiatively inefficient
accretion flows (RIAFs) in a global magnetic field (so called resistive RIAF
model) has proved its ability to account for many physical processes taking
place in such accretion flows as realized in the nuclei of the galaxies
believed to be accreting at a very small fraction of each Eddinton accretion
rate. Within the present status of this model, however, the model cannot
describe the launch of a self-confined bipolar jet from the vicinity of disk's
inner edge, although it allows the existence of a thermal wind widely
distributed over the disk surfaces. This is because the electric field (and
hence the Poynting flux) vanishes everywhere in the disk, whereas such a jet in
a globally ordered magnetic field is most likely to be accelerated
electrodynamically. We show in the present paper that this defect can be
overcome naturally if we reformulate the problem so as to admit a
quasi-stationary change of the magnetic field (and hence the appearance of a
non-irrotational electric field), and also restore all the terms of order
epsilon ~ (v_r/v_{varphi})^2 < 1 (where v_r and v_{varphi} denote radial and
azimuthal components, respectively, of the fluid velocity) which have been
neglected altogether in the previous treatments. The restored effects are the
inertial and magnetic draggings on the infalling matter. As an illustrative
example, a model solution which is correct up to the first order in epsilon is
derived under a set of plausible restrictions. The new solution predicts the
appearance of a localized Poynting flux in a region near the disk inner edge,
suggesting strongly that a jet is launched from this region. Another
interesting prediction is the appearance of a rapid change of the magnetic
field also localized to this region.
View original:
http://arxiv.org/abs/1112.0726
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