2021/05/10 by Sandeep Kumar Acharya, Jens Chluba, Abir Sarkar · 8 citations
Physics and Astronomy · #Anisotropy #Astrophysics and Cosmic Phenomena #Bremsstrahlung #Compton scattering #Computational physics #Cosmic microwave background #Electron #Galaxies: Formation, Evolution, Phenomena #Ionosphere and magnetosphere dynamics #Photon #Physics #Quantum mechanics #Scattering #astro-ph.CO #astro-ph.HE
paper · pdf · doi:10.1093/mnras/stab2259
published in Monthly Notices of the Royal Astronomical Society 507(2), 2052-2072 (Oxford University Press) · Comments welcome
arxiv created 2021/05/10 · openalex publication_date 2021/08/03 · arxiv updated 2021/08/18 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
ABSTRACT Repeated Compton scattering of photons with thermal electrons is one of the fundamental processes at work in many astrophysical plasma. Solving the exact evolution equations is hard and one common simplification is based on Fokker–Planck (FP) approximations of the Compton collision term. Here we carry out a detailed numerical comparison of several FP approaches with the exact scattering kernel solution for a range of test problems assuming isotropic media and thermal electrons at various temperatures. The Kompaneets equation, being one of the most widely used FP approximations, fails to account for Klein–Nishina corrections and enhanced Doppler boosts and recoil at high energies. These can be accounted for with an alternative FP approach based on the exact first and second moments of the scattering kernel. As demonstrated here, the latter approach works very well in dilute media, but inherently fails to reproduce the correct equilibrium solution in the limit of many scattering. Conditions for the applicability of the FP approximations are clarified, overall showing that the Kompaneets equation provides the most robust approximation to the full problem, even if inaccurate in many cases. We close our numerical analysis by briefly illustrating the solutions for the spectral distortions of the cosmic microwave background (CMB) after photon injection at redshift z ≲ 105, when double Compton and Bremsstrahlung emission can be omitted. We demonstrate that the exact treatment using the scattering kernel computed with cspack is often needed. This work should provide an important step towards accurate computations of the CMB spectral distortions from high-energy particle cascades.