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

TL;DR

This paper investigates the radiative signatures during the transition between ejector and accretor modes in neutron stars, highlighting how accretion processes and magnetic field configurations influence gamma-ray spectra.

Contribution

It introduces a simple quasi-spherical accretion model to analyze transitional states and predicts specific gamma-ray spectral features during these mode changes.

Findings

Transition states show gamma-ray spectra truncated below ~1 GeV.

Accretion modes can coexist along different magnetic field lines.

Thermal radiation from the neutron star surface modifies pulsar radiation processes.

Abstract

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.