Absorption of Gamma-Ray Photons in a Vacuum Neutron Star Magnetosphere: I. Electron-Positron Pair Production

TL;DR

This paper investigates electron-positron pair production in vacuum neutron star magnetospheres under various magnetic field strengths, highlighting the dominant role of synchrotron photons and the impact of finite acceleration time on plasma generation rates.

Contribution

It provides a detailed calculation of pair production sources considering curvature and synchrotron photons, including the effects of finite electron acceleration time.

Findings

Synchrotron photons dominate pair production in weak magnetic fields.

Finite acceleration time significantly reduces plasma generation rates.

An effective local pair production source was constructed for hydrodynamic modeling.

Abstract

The production of electron-positron pairs in a vacuum neutron star magnetosphere is investigated for both low (compared to the Schwinger one) and high magnetic fields. The case of a strong longitudinal electric field where the produced electrons and positrons acquire a stationary Lorentz factor in a short time is considered. The source of electron-positron pairs has been calculated with allowance made for the pair production by curvature and synchrotron photons. Synchrotron photons are shown to make a major contribution to the total pair production rate in a weak magnetic field. At the same time, the contribution from bremsstrahlung photons may be neglected. The existence of a time delay due to the finiteness of the electron and positron acceleration time leads to a great reduction in the electron-positron plasma generation rate compared to the case of a zero time delay. The effective local source of electron-positron pairs has been constructed. It can be used in the hydrodynamic equations that describe the development of a cascade after the absorption of a photon from the cosmic gamma-ray background in a neutron star magnetosphere.