No abstract

The luminosity of X-ray pulsars powered by accretion onto magnetized neutron stars covers a wide range over a few orders of magnitude. The brightest X-ray pulsars recently discovered as pulsating ultraluminous X-ray sources reach accretion luminosity above 10 40 erg s −1 which exceeds the Eddington value more than by a factor of ten. Most of the energy is released within small regions in the vicinity of magnetic poles of accreting neutron star -in accretion columns. Because of the extreme energy release within a small volume accretion columns of bright X-ray pulsars are ones of the hottest places in the Universe, where the internal temperature can exceed 100 keV. Under these conditions, the processes of creation and annihilation of electron-positron pairs can be influential but have been largely neglected in theoretical models of accretion columns. In this letter, we investigate properties of a gas of electron-positron pairs under physical conditions typical for accretion columns. We argue that the process of pairs creation can crucially influence both the dynamics of the accretion process and internal structure of accretion column limiting its internal temperature, dropping the local Eddington flux and increasing the gas pressure.

URCA neutrino reemission processes under the conditions in the mantle of a supernova with a strong toroidal magnetic field are investigated. It is shown that parity violation in these processes can be manifested macroscopically as a torque that rapidly spins up the region of the mantle occupied by such a field. Neutrino spin-up of the mantle can strongly affect the mechanism of further generation of the toroidal field, specifically, it can enhance the field in a small neighborhood of the rigid-body-rotating core of the supernova remnant.

The interaction of neutrinos with nucleons in the envelope of a remnant of collapse with a strong magnetic field during the passage of the main neutrino flux is investigated. General expressions are derived for the reaction rates and for the energy-momentum transferred to the medium through the neutrino scattering by nucleons and in the direct URCA processes. Parameters of the medium in a strong magnetic field are calculated under the condition of quasiequilibrium with neutrinos. Numerical estimates are given for the neutrino mean free paths and for the density of the force acting on the envelope along the magnetic field. It is shown that in a strong toroidal magnetic field, the envelope region partially transparent to neutrinos can acquire a large angular acceleration on the passage time scales of the main neutrino flux. PACS: 95.30. Cq, 13.15.+q, 97.60.Bw

Based on the magnetar model, we have studied in detail the processes of neutrino cooling of an electron-positron plasma generating an SGR giant flare and the influence of the magnetar magnetic field on these processes. Electron-positron pair annihilation and synchrotron neutrino emission are shown to make a dominant contribution to the neutrino emissivity of such a plasma. We have calculated the neutrino energy losses from a plasma-filled region at the long tail stage of the SGR 0526-66, SGR 1806-20, and SGR 1900+14 giant flares. This plasma can emit the energy observed in an SGR giant flare only in the presence of a strong magnetic field suppressing its neutrino energy losses. We have obtained a lower bound on the magnetic field strength and showed this value to be higher than the upper limit following from an estimate of the magnetic dipole losses for the magnetars being analyzed in a wide range of magnetar model parameters. Thus, it is problematic to explain the observed energy release at the long tail stage of an SGR giant flare in terms of the magnetar model.