2008 Supplement: Frascati Workshop 2007 / Šimon

Long-term Variations of Soft X-ray Transients

V. Šimon

Abstract

We concentrate on several items of long-term activity of soft X-ray
transients (SXTs). The existence of known neutron star (NS) SXTs
is not dependent on the orbital period P_{orb}, which indicates a
large scatter of the mass transfer rate in low-mass X-ray binaries
of a given P_{orb}. We investigate the role of irradiation of the disk
on several examples of SXTs and show the cases when it evolves
during outburst. We interpret the variations of the recurrence time
T_{C} of outbursts of Aql X-1 and 4U 1608-52; the outbursts are
triggered near the optically thin ADAF region and propagate outward
in the disk. The outer disk region is brought to the hot state only in
the rare, most intense outbursts. The amount of mass accreted largely
varies for the individual outbursts in a given SXT. We also argue that
the change of T_{C} in the Rapid Burster is caused by an increase of
the disk viscosity. The cyclic modulation of T_{C} of GRS 1747-312 can
suggest stellar activity of the donor. We interpret the so-called echo
outbursts in KS 1731-260 as a series of outside-in outbursts, dependent
on each other.

Keywords


Stars: neutron accretion accretion disks binaries: close circumstellar matter X-rays: binaries

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