Enhanced Bremsstrahlung from Supraluminous, and Subluminous, Waves in an Isotropic, Homogeneous Plasma

A calculation is presented of the bremsstrahlung radiation from a thermal, Maxwellian electron plasma which may have an isotropic, relativistic, (non-Maxwellian) tail. The calculation assumes homogeneity, isotropy, the absence of any imbedded ambient magnetic fields, and a smeared out distribution of ions which serves to preserve over-all space charge neutrality, but does not take part in any motion. When allowance is made for the fact that no particles resonate with waves whose phase velocity exceeds the speed of light, it is demonstrated that the “character” of the emission changes sharply at ω = ck. Provided the electron temperature is less than about 108 °K, it is shown that the supraluminous (ω > ck) bremsstrahlung from the thermal electrons dominates the subluminous (ω < ck) radiation from the same particles. It is also shown that a few relativistic electrons can act as a “catalyst,” greatly enhancing the subluminous bremsstrahlung but hardly influencing the supraluminous bremsstrahlung. The enhanced emission occurs at, and at twice, the electron plasma frequency. Using numerical values appropriate to the Crab nebula, it is shown that the enhanced subluminous bremsstrahlung can easily dominate the synchrotron radiation and the usual “collisional” bremsstrahlung at, and at twice, the electron plasma frequency. Also the enhanced supraluminous emission due to static “bumps” in the plasma is shown to exceed other conventional radiation processes in the Crab nebula.