Publications
of the
MPIfR
Optical & Infrared
Interferometry Group
N.R. Ikhsanov, V.M. Larionov and N.G.
Beskrovnaya:
On the accretion flow geometry in A0535+26
Astronomy & Astrophysics 372, 227-232
(2001)
Abstract.
The geometry of accretion flow in the Be/X-ray transient A0535+26 is
explored. It is shown that neither moderate nor giant X-ray flaring
events observed in the system can be interpreted within the
spherically symmetrical accretion model and hence the formation of
an accretion disk around the neutron star magnetosphere during the
both types of flares is required. The accretion disk can be formed
at the periastron if (i) the expansion velocity of the
Be star envelope in the equatorial plane is Vwr < 150
km/s
and (ii) the parameter accounting for the accretion
flow inhomogeneities, xi, satisfies the following condition:
xi > 0.16 Mdot17-1/7, where Mdot17-1/7
is the rate of mass capture by the neutron star expressed in units
of 1017 g/s.
We suggest that the `missing' outburst phenomenon can be associated
with the spherically symmetrical accretion onto the interchange-stable
magnetosphere of the neutron star. The average spin up rate
of the neutron star during moderate flares < 3.5 x 10-12
Hz/s is predicted.
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