Association of centimeter-wave bursts with different spectral types of meter-wave bursts of solar radio emission

Abstract

It is shown that about 40 per cent of 10.7 cm-λ bursts with peak intensities greater than 5×10−22 wm−2 (c/s)−1 are accompanied by bursts on meter waves. The percentage association increases with the peak intensity of 10.7 cm-λ bursts and attains a value of about 90 per cent when the peak intensity exceeds 1000×10−22 wm−2 (c/s)−1. The reverse association, that is, the association of a meter-λ burst with a burst on centimeter waves, is dependent on the spectral type of the meter-λ burst. The association is about 15, 40, 70, and 100 per cent for types III, V, II, and IV, respectively. The type III and type V bursts usually occur within about 1 minute and ½ minute, respectively, of the associated cm-λ burst maxima. The type II bursts occur after about 2 to 6 minutes of the associated cm-λ burst maxima. The type IV bursts in the 250 to 580 Mc/s range occur within about 4 minutes of the start of the associated cm-λ bursts. From simultaneous dynamic spectral observations in the 25 to 580 Mc/s range and single-frequency observations on 9400, 3750, 2000, and 1000 Mc/s, the average spectra of cm-λ bursts associated with different spectral types of meter-λ bursts have been studied. It is shown that cm-λ bursts associated with meter-λ type IV and type II bursts have brightness temperatures of the order of 108 and 107 deg K, respectively, and can probably be explained by synchrotron radiation of high-energy electrons. The cm-λ bursts associated with type V and type III bursts have brightness temperatures of 106 to 107 deg K in the 2000 to 9400 Mc/s range and have probably a thermal plus synchrotron origin; the 1000 Mc/s bursts have brightness temperatures higher than 107 deg K and have a nonthermal origin, probably due to plasma oscillation corresponding to type III bursts. The cm-λ bursts unaccompanied by any meter-λ burst have brightness temperatures less than 106 deg K and are believed to have a thermal origin.