Sub-second pulsations simultaneously observed at microwaves and hard X rays in a solar burst

Sub-second time structures have been found in millimetre waves 1,2 and, independently, in hard X rays 3,4 emitted during solar bursts. However, because simultaneous observations of such fast time structures in millimetre radio and X-ray ranges had not been available, we planned coordinated observations of the solar burst in November 1981 with a high time resolution of a few milliseconds. The hard X rays (30–40 keV) were observed by the hard X-ray monitor, HXM 5 , aboard the Hinotori Satellite with a time resolution of 7.81 ms and the radio emissions were observed on the ground by the 45-ft dish at Itapetinga Radio Observatory with a high time resolution (1 ms) and high sensitivities at 22 GHz and 44 GHz (ref. 6), supplemented by patrol observations at 7 GHz with a time resolution of 100 ms. Absolute timing at Itapetinga and Hinotori is better than 10 ms. Correlated sub-second time structures at hard X-ray and at millimetre wavelengths were found for the first time.