Wind-accreting symbiotic X-ray binaries

Abstract

© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. We present a new model of the population of symbiotic X-ray binaries (SyXBs) that takes into account the non-stationary character of quasi-spherical sub-sonic accretion of the red giant's stellar wind on to slowly rotating neutron stars (NSs). Updates of the earlier models are given, which include more strict criteria of slow NS rotation for plasma entry into the NS magnetosphere via the Rayleigh-Taylor instability, as well as more strict conditions for settling accretion for slow stellar winds, with an account of variations in the specific angular momentum of captured stellar wind in eccentric binaries. These modifications enabled a more adequate description of the distributions of observed systems over binary orbital periods, NS spin periods, and their X-ray luminosity in the ∼1032-1036 erg s-1 range and brought their model Galactic number into reasonable agreement with the observed one. Reconciliation of the model and observed orbital periods of SyXBs requires a low efficiency of matter expulsion from common envelopes during the evolution that results in the formation of NS components of symbiotic X-ray systems.