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Title: "Orbital and super-orbital variability of X-ray binaries"
Prof. Andrzej Zdziarski
CAMK, Warsaw, Poland

When:  Wednesday 6 May 2009 at 3:15pm
Where: 2nd Floor Seminar Room

Abstract:

I will review flux modulation from X-ray binaries on time scales
corresponding to the orbital period and those at longer time scales
(so called superorbital). Those modulations provide a powerful tool to
constrain geometry of the accretion flow. The most common cause of the
superorbital variability is precession. I will then discuss two
specific examples of discoveries of a coupling between the two
variabilities and its physical interpretation. One is Cyg X-1, a
black-hole binary with a high-mass companion, in which case we found
the presence of an accretion bulge formed by collision of the stellar
wind with the outer edge of the accretion disc. The other is 4U
1820-303, a neutron star accreting from a low-mass white dwarf, in
which case we interpret the superorbital variability as accretion rate
modulation appearing in a triple stellar system.
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