# Mean opacities of a strongly magnetized high temperature plasma

**Authors:** Valery F. Suleimanov, Alexander A. Mushtukov, Igor Ognev, Victor A. Doroshenko, Klaus Werner  
**arXiv:** [2210.09995](https://arxiv.org/abs/2210.09995)  
**Date:** 2022-10-18  
**Summary page:** https://www.summarizepaper.com/en/paper/2210.09995v1/

## Key points

- In accreting pulsars, gravity, radiation, and strong magnetic fields shape emission regions
- The interplay between these factors affects plasma opacities and radiative pressure
- Quantitative magnetic plasma opacities are essential for self-consistent modeling of emission region structures in X-ray pulsars
- The authors computed Rosseland and Planck mean opacities of a strongly magnetized plasma with a simple chemical composition (solar hydrogen/helium mix)
- They considered all relevant specific opacities, including vacuum polarization effects and contributions from electron-positron pairs
- Magnetic Planck mean opacity determines radiative cooling of optically thin strongly magnetized plasma
- It is three times smaller than non-magnetic Planck opacity at low temperatures but increases by a factor of $10^2 - 10^4$ at high temperatures due to cyclotron thermal processes
- The authors propose an approximate expression that accurately describes magnetic Planck opacity
- Rosseland opacity is provided in tabular form for temperature range 1 - 300 keV, magnetic field range $3 \times 10^{10} - 10^{15}$ G, and a broad range of plasma densities
- Scattering on electron-positron pairs increases Rosseland opacity drastically at temperatures above 50 keV for mass densities typical for accretion channels in X-ray pulsars.
- Magnetic plasma opacities are important when modeling emission region structures in X-ray pulsars as they affect both radiative cooling and radiative pressure under extreme conditions.

## Summary

In accreting pulsars, the interplay between gravity, radiation, and strong magnetic fields shapes the geometry and dynamical structure of emission regions. This interplay significantly affects the opacities of a plasma and radiative pressure under such extreme conditions. Therefore, it is essential to consider quantitative magnetic plasma opacities in any self-consistent modeling of emission region structures in X-ray pulsars. In this study, the authors present computations of Rosseland and Planck mean opacities of a strongly magnetized plasma with a simple chemical composition, namely the solar hydrogen/helium mix. They consider all relevant specific opacities of the magnetized plasma, including vacuum polarization effects and contributions from electron-positron pairs where the pair number density is computed in thermodynamic equilibrium approximation. The magnetic Planck mean opacity determines the radiative cooling of an optically thin strongly magnetized plasma. The authors find that it is three times smaller than non-magnetic Planck opacity at $k_{\rm B}T < 0.1\,E_{\rm cyc}$ and increases by a factor of $10^2 - 10^4$ at $k_{\rm B}T > 0.3\,E_{\rm cyc}$ due to cyclotron thermal processes. They propose a simple approximate expression that accurately describes magnetic Planck opacity. The authors provide Rosseland opacity in tabular form computed in the temperature range 1 - 300 keV, magnetic field range $3 \times 10^{10} - 10^{15}$ G, and a broad range of plasma densities. They demonstrate that scattering on electron-positron pairs increases Rosseland opacity drastically at temperatures above 50 keV for mass densities typical for accretion channels in X-ray pulsars. Overall, this study highlights how important it is to consider magnetic plasma opacities when modeling emission region structures in X-ray pulsars as they affect both radiative cooling and radiative pressure under extreme conditions. The presented results provide valuable insights into the opacities of strongly magnetized plasmas and can aid in developing more accurate models of emission regions in accreting pulsars.