Z. Kuncic et Pa. Robinson, PROPAGATION AND ABSORPTION OF CYCLOTRON MASER RADIATION IN SOLAR MICROWAVE SPIKE BURSTS, Solar physics, 145(2), 1993, pp. 317-338
It has been argued that the loss-cone-driven electron cyclotron maser
instability can account for the properties of millisecond microwave sp
ike bursts observed during some solar flares. However, as it propagate
s outward from the corona, maser radiation undergoes gyroresonance abs
orption when its frequency is a harmonic of the local electron-cyclotr
on frequency. Existing analytical models using slab geometries predict
that this absorption should be sufficiently strong to prevent the rad
iation from being seen at the observed levels, except under highly res
trictive conditions or for unrealistic plasma parameters. A more compr
ehensive analysis is presented here to determine if and when maser rad
iation can escape to produce microwave spike bursts. This analysis emp
loys numerical raytracing and incorporates propagation and absorption
of fundamental maser emission in a realistic model of a coronal flux l
oop. It is found that ranges of physical conditions do exist under whi
ch maser radiation can escape to an observer and that these conditions
are much more limiting for fundamental emission in the extraordinary
(x)-mode than in the ordinary (o)-mode. Detailed investigation implies
that escaping radiation in the x-mode is highly directional and chief
ly observable toward the center of the solar disk, while escaping o-mo
de radiation is found to emerge from the corona over a much wider rang
e of directions, with some cases corresponding to radiation observable
near the solar limb.