EDP Sciences
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Volume 367, Number 2, February IV 2001
Page(s) 549 - 556
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20000464

A&A 367, 549-556 (2001)
DOI: 10.1051/0004-6361:20000464

On the origin of quiescent X-ray emission from A0535+26

N. R. Ikhsanov1, 2

1  Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
2  Central Astronomical Observatory of the Russian Academy of Science at Pulkovo, Pulkovo 65-1, 196140 Saint-Petersburg, Russia

(Received 9 October 2000 / Accepted 5 December 2000)

The quiescent X-ray emission from A0535+26 ( $L_{\rm x}\sim 2 10^{35} \rm erg s^{-1}$) is explored in terms of the spherically symmetrical accretion onto a magnetized neutron star. I find the magnetospheric boundary of the neutron star in A0535+26 to be stable with respect to interchange instabilities. The fastest mode by which the accreting plas ma can enter the magnetosphere is the magnetic lines reconnection. Under this condition the quiescent X-ray luminosity of the system can be explained provided the mass capture rate by the neutron star from the wind of the Be companion of $\sim$ $10^{-9} M_{\odot} {\rm yr}^{-1}$. I show this value to be in a good agreement with the mass capture rate independently evaluated from the established parameters of the Be star circumstellar environment. The suggested approach allows to interpret the low luminous state of the system ( $L_{\rm x} \sim 4 10^{33} \rm erg s^{-1}$) in August -November 1998 in terms of the accretion powered pulsar model. I find the mass capture rate by the neutron star during this time of $3 10^{-11} M_{\odot} {\rm yr}^{-1}$. This can be realized provided the plasma density in the circumstellar disk of the Be companion is by two orders of magnitude smaller than its average value. Under this condition the disk is expected to be invisible in the optical/IR.

Key words: accretion -- magnetic fields -- stars: close binaries -- stars: Be -- stars: neutron star

Offprint request: N. R. Ikhsanov, ikhsanov@mpifr-bonn.mpg.de

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