O. D. Toropina, M. M. Romanova, R. V. E. Lovelace
Axisymmetric MHD simulations are used to investigate the Bondi-Hoyle
accretion onto an isolated magnetized neutron star moving supersonically (with
Mach number of 3) through the interstellar medium. The star is assumed to have
a dipole magnetic field aligned with its motion and a magnetospheric radius R_m
less then the accretion radius R_BH, so that the gravitational focusing is
important. We find that the accretion rate to a magnetized star is smaller than
that to a non-magnetized star for the parameters considered. Close to the star
the accreting matter falls to the star's surface along the magnetic poles with
a larger mass flow to the leeward pole of the star. In the case of a relatively
large stellar magnetic field, the star's magnetic field is stretched in the
direction of the matter flow outside of R_m (towards the windward side of the
star). For weaker magnetic fields we observed oscillations of the closed
magnetosphere frontward and backward. These are accompanied by strong
oscillations of the mass accretion rate which varies by factors ~ 3. Old slowly
rotating neutron stars with no radio emission may be visible in the X-ray band
due to accretion of interstellar matter. In general, the star's velocity,
magnetic moment, and angular velocity vectors may all be in different
directions so that the accretion luminosity will be modulated at the star's
rotation rate.
View original:
http://arxiv.org/abs/1111.2460
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