Complex Topology of the Magnetic Field in Strong Flares

We report the "5+1" dynamical classification of the most frequently observed topologies of the magnetic field in sunspot groups associated with powerful flares.Comment: 2 pages, 1 figure, Proceedings of IAU Symp. 223, Volume 2004, page 25

Supersonic propeller spindown of neutron stars in wind-fed mass-exchange close binaries

The supersonic propeller spindown of a neutron star moving in a strong stellar wind of its massive companion is discussed. I show that the supersonic propeller model presented by Davies & Pringle (1981}) is self-consistent if the strength of the stellar wind of the normal companion is \dot{M}_{\rm c} \la 2.2 10^{18} (M_{\rm ns}/M_{\sun}) V_8 g/s. Under these conditions the model can be used for the interpretation of the long-period pulsars in Be/X-ray transients. The spin history of the neutron star in the long period Be/X-ray transient A0535+26 is considered.Comment: 3 pages, published in A&A Letters 381, L61 (2002

On the magnetic fields of Be/X-ray pulsars in the Small Magellanic Cloud

We explore the possibility to explain the properties of the Be/X-ray pulsars observed in the Small Magellanic Cloud within the magnetic levitation accretion scenario. This implies that their X-ray emission is powered by a wind-fed accretion onto a neutron star (NS) which captures matter from a magnetized stellar wind. The NS in this case is accreting matter from a non-keplerian magnetically levitating disc (ML-disc) which is surrounding its magnetosphere. This allows us to explain the observed periods of the pulsars in terms of spin equilibrium without the need of invoking dipole magnetic fields outside the usual range ~ 10^11- 10^13 G inferred from cyclotron features of Galactic high mass X-ray binaries. We find that the equilibrium period of a NS, under certain conditions, depends strongly on the magnetization of the stellar wind of its massive companion and, correspondingly, on the magnetic field of the massive companion itself. This may help to explain why similar NSs in binaries with similar properties rotate with different periods yielding a large scatter of periods of the accretion-powered pulsar observed in SMC and our galaxy.Comment: 6 pages, 1 figure, Published in MNRAS 454, 3760-3765 (2015

Subsonic propellers in a strong wind as anomalous X-ray pulsars

The appearance of subsonic propellers situated in a strong wind is discussed. We show that it is similar to the appearance of anomalous X-ray pulsars (AXPs) provided the mass and the magnetic moment of neutron stars are 1.4 solar masses, and 2E+30 G cm^3, respectively, and the strength of the wind is M_c = 3E+17 g/s. Under these conditions, the spin periods of subsonic propellers are limited within the range of 5-15 s, and the expected spin-down rates are close to 7E-11 s/s. The mass accretion rate onto the stellar surface is limited to the rate of plasma penetration into its magnetosphere at the boundary. As this process is governed by the reconnection of the field lines, the accretion rate onto the stellar surface constitutes 1-2% of M_c. In this case the X-ray luminosity of the objects under consideration can be evaluated as 4E+35 erg/s. The model predicts the existence of at least two spatially separated sources of the X-ray emission: hot spots at the stellar surface, and the hot atmosphere surrounding the magnetosphere of the star. The ages of the subsonic propellers under the conditions of interest are limited to 10^5 yr.Comment: 5 pages, 1 figure, accepted for publication in A&