# Electron-positron pairs in hot plasma of accretion column in bright X-ray pulsars

## TL;DR

This paper investigates how electron-positron pair creation affects the dynamics and structure of accretion columns in bright X-ray pulsars, potentially limiting temperature and influencing accretion physics.

## Contribution

It introduces the consideration of pair creation processes into models of accretion columns, highlighting their significant impact on temperature, pressure, and luminosity limits.

## Key findings

- Pair creation can limit the internal temperature of accretion columns.
- Electron-positron pairs influence the pressure and structure of the accretion flow.
- Pair processes may reduce the local Eddington flux in accretion columns.

## 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 $10^{40}\,{\rm erg\,s^{-1}}$ 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.