The bremsstrahlung emissivity and absorption coefficient in the
radiofrequency range are derived under
the assumption that the electron population is not purely thermal, but
presents a tail of high energy particles.
This population is approximated by a two-component Maxwellian
distribution and by the kappa-functions of different (integer) index.
It is shown that, if the temperature ratio
of the two Maxwellians is larger than 10, the absorption coefficient
and the effective temperature (the quantities entering the radio
transfer equation) depend
only on the fraction R of particles in the highest temperature Maxwellian.
In the case of kappa-functions the above quantities depend on the index n of
the functions. The microwave radio spectrum is computed for different values of R and
for 3≤n≤6, finding, in all cases,
brightness temperatures lower than those computed with a pure thermal
distribution. This could explain some inconsistencies found between
radio and EUV observations
