Publications
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MPIfR Optical & Infrared Interferometry Group

N.R. Ikhsanov, N.G. Beskrovnaya, V.M. Larionov:

Accretion flow geometry during fares in A0535+26

Astronomische Gesellschaft Abstract Series (AGM 18, P63)
Five Days of Creation: Astronomy with Large Telescopes from Ground and Space
Annual Scientific Meeting of the Astronomische Gesellschaft at the Joint European and National Meeting JENAM 2001 of the European Astronomical Society and the Astronomische Gesellschaft, Sep 10-15, 2001, Munich, Germany

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-1 and (ii) the parameter accounting for the accretion flow inhomogeneities, ξ, satisfies the following condition: ξ > 0.16 dot{M}17-1/7, where dot{M}17 is the rate of mass capture by the neutron star expressed in units of 1017 g s-1. 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 × 10-12 Hz s-1 is predicted.

bloecker@mpifr-bonn.mpg.de.
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