Collective Plasma Radiation Processes

Abstract

Specifically, brightness temperatures much greater than the energy of the radiating particles (TB» 101 0 K) imply some form of coherent emission. (With Boltzmann's constant set equal to unity, temperatures are expressed in energy units with I eV = 1.16 x 104K.) Four classes ofradio astronomical sources are known to require coherent emission mechanisms. These are, in order of their discovery, (a) solar radio bursts, the most widely studied of which are type III bursts (TB:S 1015 K); (b) the decametric radio emission from Jupiter (TB <: 1017 K) and related emission from other planets, notably the auroral kilometric radiation (AKR) from the Earth; (c) maser emission in OH and other molecular lines from interstellar and circum stellar clouds (TB:S 1015 K); and (d) pulsar radio emission (TB ;$ 1030 K). Maser line emission is clearly not due to a collective plasma emission process and is not discussed here. Thus three coherent mech­ anisms are relevant: plasma emission from the solar corona and possibly from other sources; electron cyclotron maser emission (ECME) from the planets, the Sun, and some flare stars; and pulsar radio emission. Progress has been made over the last decade or so in the theories for each of these coherent emission processes. The literature is diverse, however, and it is difficult to identify any major characteristic theme. To give this review a structure and theme, emphasis is placed on models for