Outstanding Solar Radio Burst at 4.2 mm

Abstract

ALTHOUGH the Sun has been studied extensively over a wide range of radio-wavelengths for 20 yr, until recently there have been very few observations at wavelengths of less than 3 cm and even fewer at wavelengths of less than 1 cm (that is, in the millimetre band). We report here the observation of a major radio burst at 4.2 mm (71 GHz) and 16 mm (19 GHz). This burst, which was associated with a class 2B flare¹ at 0944 UT on July 6, 1968, may be the largest ever recorded at millimetre wavelengths, and in any case ranks among the largest bursts ever observed at any wavelength². It is particularly interesting to note that at the most commonly used solar-monitoring wavelength in the microwave band (10.7 cm) the burst was only of very moderate intensity. The details of the burst, as recorded at the Slough Solar Radio Observatory (51° 29′ 1ST, 0° 34′ W), are given in Table 1 and Fig. 1. (The 10.7 cm data were provided by Mr A. Cribbens of University College, London.)