High energy signatures of quasi-spherical accretion onto rotating, magnetized neutron star in the ejector-accretor intermediate state

We consider a simple scenario for the accretion of matter onto a neutron star in order to understand processes in the inner pulsar magnetosphere during the transition stage between different accretion modes. A simple quasi-spherical accretion process onto rotating, magnetized compact object is analyzed in order to search for the radiative signatures which could appear during transition between ejecting and accreting modes. It is argued that different accretion modes can be present in a single neutron star along different magnetic field lines for specific range of parameters characterising the pulsar (rotational period, surface magnetic field strength) and the density of surrounding medium. The radiation processes characteristic for the ejecting pulsar, i.e. curvature and synchrotron radiation produced by primary electrons in the pulsar outer gap, are expected to be modified by the presence of additional thermal radiation from the neutron star surface. We predict that during the transition from the pure ejector to the pure accretor mode (or vice versa) an intermediate accretion state can be distinguished which is characterized by the $\gamma$-ray spectra of pulsars truncated below ~1 GeV due to the absorption of synchro-curvature spectrum produced in the pulsar gaps.Comment: 12 pages, 4 figures, accepted to Journal of High Energy Astrophysic

Structure and properties of neutron stars in the Relativistic Mean - Field Theory

Properties of rotating neutron stars with the use of relativistic mean-field theory are considered. The performed analysis of neutron star matter is based on the nonlinear Lgrangian density. The presence of nonlinear interaction of vector mesons modifies the density dependence of the rho field and influences bulk parameters of neutron stars. The observed quasi-periodic X-ray oscillations of low mass X-ray binaries can be used in order to constrain the equation of state of neutron star matter. Having assumed that the maximum frequency of the quasi periodic oscillations originates at the circular orbit it is possible to estimate masses and radii of neutron stars.Comment: 18 pages, latex2e, 10 colour eps figures, submitted to International Journal of Modern Physic