2015/10/21 by Vahé Petrosian, Byungwoo Kang · 8 citations
Physics and Astronomy · #Acceleration #Astrophysical Phenomena and Observations #Astrophysics and Cosmic Phenomena #Bremsstrahlung #Electron #Kinetic energy #Particle acceleration #Scattering #Solar and Space Plasma Dynamics #Solar flare #Thermal #astro-ph.HE
paper · pdf · doi:10.1088/0004-637x/813/1/5
published in The Astrophysical Journal 813(1), 5 (IOP Publishing) · 21 pages, 9 figures, accepted for publication in ApJ
openalex publication_date 2015/10/21 · arxiv created 2016/04/24 · arxiv updated 2016/04/26 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We investigate heating and acceleration of protons from a thermal gas with a generic diffusion and acceleration model, and subject to Coulomb scattering and energy loss, as was done by Petrosian & East for electrons. As protons gain energy their loss to electrons becomes important. Thus, we need to solve the coupled proton–electron kinetic equation. We numerically solve the coupled Fokker–Planck equations and compute the time evolution of the spectra of both particles. We show that this can lead to a quasi-thermal component plus a high-energy nonthermal tail. We determine the evolution of the nonthermal tail and the quasi-thermal component. The results may be used to explore the possibility of inverse bremsstrahlung radiation as a source of hard X-ray emissions from hot sources such as solar flares, accretion disk coronas, and the intracluster medium of galaxy clusters. We find that the emergence of nonthermal protons is accompanied by excessive heating of the entire plasma, unless the turbulence needed for scattering and acceleration is steeper than Kolmogorov and the acceleration parameters, the duration of the acceleration, and/or the initial distributions are significantly fine-tuned. These results severely constrain the feasibility of the nonthermal inverse bremsstrahlung process producing hard X-ray emissions. However, the nonthermal tail may be the seed particles for further re-acceleration to relativistic energies, say by a shock. In the Appendix we present some tests of the integrity of the algorithm used and present a new formula for the energy loss rate due to inelastic proton–proton interactions.