Avalanche photon cooling by induced Compton scattering: Higher-order Kompaneets equation

摘要

Induced Compton scattering (ICS) is an interaction between intense electromagnetic radiation and plasmas, where ICS transfers the energy from photons to plasma. Although ICS is important for laser plasma interactions in laboratory experiments and for radio emission from pulsars propagating in pulsar wind plasmas, the detail of the photon cooling process has not been understood. The problem is that, when ICS dominates, the evolution of photon spectra is described as a nonlinear convection equation, which makes the photon spectra multi-valued. Here, we propose a new approach to treat the evolution of photon spectra affected by ICS. Starting from the higher-order Kompaneets equation, we find a new equation that resolves the unphysical behavior of photon spectra. In addition, we find the steady-state analytic solution, which is linearly stable. We also successfully simulate the evolution of photon spectra without artificial viscosity. We find that photons rapidly lose their energy by ICS with continuously forming solitary structures in frequency space. The solitary structures have the same logarithmic width characterized by an electron temperature. The energy transfer from photons to plasma is more effective for a broader spectrum of photons such as that expected in astrophysical situations.