Abstact: The wind-fed accretion of magnetized gas onto a neutron star in a high-mass X-ray binary system (HMXB) is discussed. The criteria for the implementation of quasi-spherical accretion in the system, the formation of a Keplerian accretion disk and a non-Keplerian magnetically arrested disk (MAD-accretion scenario) are formulated. It is shown that the period of equilibrium rotation of the neutron star in the MAD-accretion scenario, in addition to the parameters of the binary system, is determined by the velocity, temperature, and degree of magnetization of the stellar wind of its massive companion. Within the hypothesis of the equilibrium rotation, we have estimated the parameters of the stellar wind for the most fully-studied quasi-equilibrium accreting pulsars in the HMXBs corresponding to the criteria for the MAD-accretion scenario implementation. We show that the equilibrium period of an accretion-powered pulsar under the same conditions increases with the growth of the magnetization of the accretion flow. Therefore, the periods of accreting pulsars in the systems with similar parameters can differ from each other by several orders of magnitude and, under favorable conditions, reach values of several thousand and even tens of thousands of seconds. A realization of the MAD-accretion scenario in AGNs is also briefly discussed.
Short bio: Nazar Ikhsanov is the Director of the Central Astronomical Observatory of the Russian Academy of Sciences at Pulkovo (Pulkovo Observatory, Saint-Petersburg, Russia). MS (the Leningrad State University in 1986) and PhD (the Pulkovo Observatory in 1989). Career milestones: an Alexander von Humboldt Fellow at the Ludwig-Maximilian University (Munich, Germany) and at the Max Planck Institute for Radioastronomy (Bonn, Germany); a Research Fellow at the Korea Astronomy and Space Science Institute (Daejeon, South Korea); Maria Curie Fellow at the Institute of Astronomy of the University of Cambridge (Cambridge, UK); NPP Program Senior Fellow at the Marshal Space Flight Center (Huntsville, AL, US). In 2011-2016 is a Head of the Stellar Evolution Dept. of Pulkovo Observatory and a Professor of Astronomy of the Saint-Petersburg State University. From 2016 is the Director of Pulkovo Observatory. Main topics of research are magneto-rotational evolution of degenerate stars, accretion in close binaries and AGNs and flaring activity of astrophysical objects.