Particle acceleration and electromagnetic field of deformed neutron stars

Abstract

Neutron stars (NS)s are astrophysical objects with strong gravitational and electromagnetic fields. Since there are several effects on radiation processes around the star, it is impossible to consider whole effects all together. One way to study the processes is by considering them one by one as a toy model. In this paper, we have investigated the effects of spacetime deformation on the surface magnetic field of the slowly rotating neutron star and its plasma magnetospheric processes, such as the plasma magnetosphere formation around the star. At first, the approximate vacuum solutions of the Maxwell equations for the electromagnetic fields of a magnetized neutron star in a slowly rotating deformed spacetime metric have been obtained. It has been shown that the positive deformation parameter leads to an increase in the value of the (surface) magnetic field at the near zone of the neutron star, while the effect of the negative deformation parameter is vice versa. We have also considered the electric field of the slowly rotating neutron star in the spacetime. In the slow rotation approximation, we have studied the particle acceleration in the polar cap zone, considering the effect of deformation of spacetime on the [Formula: see text]-Lorentz factor of a relativistic charged particle. It is shown that in the case of the positive deformation, an additional gravity occurs around the NS. The effects of spacetime deformation on magneto-dipolar radiation of radio pulsars and polar cap size have also been studied and shown that negative deformation of spacetime increased the radiation luminosity and as positive deformation increases, the luminosity decreases. Size of polar cap region of a neutron star, where magnetic field lines open, increases with increasing the value of the deformation parameter [Formula: see text]. Moreover, we have studied the influence of the spacetime deformation on the death line for radio pulsar, which separates the region in [Formula: see text] [Formula: see text] diagram, where the pulsar can or cannot radiate in radio band (create pair production) through inverse compton scattering (ICS). It is shown that the negative (positive) deformation shifts upward (downward) the death line, which means that even a small negative (positive) deformation of spacetime may cause to be radio-quite (be radio load) the radio pulsar which is lying on the death line (in [Formula: see text] diagram) in the GR frame with its corresponding parameters.