Mean opacities of a strongly magnetized high temperature plasma
Authors: Valery F. Suleimanov, Alexander A. Mushtukov, Igor Ognev, Victor A. Doroshenko, Klaus Werner
AI-generated 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.
Abstract: Geometry and dynamical structure of emission regions in accreting pulsars are shaped by the interplay between gravity, radiation, and strong magnetic field, which significantly affects the opacities of a plasma and radiative pressure under such extreme conditions. Quantitative consideration of magnetic plasma opacities is, therefore, an essential ingredient of any self-consistent modeling of emission region structure of X-ray pulsars. We present results of computations of the Rosseland and Planck mean opacities of a strongly magnetized plasma with a simple chemical composition,namely the solar hydrogen/helium mix. We consider all relevant specific opacities of the magnetized plasma including vacuum polarization effect and contribution of electron-positron pairs where the pair number density is computed in the thermodynamic equilibrium approximation. The magnetic Planck mean opacity determines the radiative cooling of an optically thin strongly magnetized plasma. It is by factor of three 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. We propose a simple approximate expression which has sufficient accuracy for the magnetic Planck opacity description. We provide the Rosseland opacity in a 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. We demonstrate that the scattering on the electron-positron pairs increases the Rosseland opacity drastically at temperatures >50 keV in the case of mass densities typical for accretion channel in X-ray pulsars.
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