The spectrum of coronal sources at millimetre and centimetre waves

Recently recognized solar millimetre-wave off-limb sources are interpreted as a special phenomenon of long-duration post- and inter-flare emission at coronal altitudes. We present, for the first time, information about the brightness and polarization spectrum in the centimetre range for one such event of September 22, 1980 by means of RATAN-600 observations.The brightness temperatures observed favour the interpretation of the bulk of the emission by thermal optically thin bremsstrahlung. The degree of polarization measured (p 0.1–0.2 in the range 7.5–15 GHz) implies quite strong magnetic fields of about 300 ± 100 G at a height z > 3 × l0⁴km above the photosphere and indicates a possible contribution of gyromagnetic radiation and/or optically thick bremsstrahlung at longer wavelengths.