CHARACTERESTICS OF A SOLAR HARD X-RAY BURST

In this paper,a very intense high-energy event occurred on April 27,1981 is analysed.Observations on SMM/GRS and radiometers at Purple Mountain Observatory reveales the onc-to-one correspondence of individul spikes in the time profiles of the hard X-rays (HXR),γ-rays and microwaves (MW) in the maximum phase.The main characteristics of the spikes are as follows: (1) The time profiles at Mm channnel (0.3-1.1MeV) of γ-rays is simira to that at higher frequence (35GHz) of MW;(2) Tie duration of individual spikes are in 66-168 second range,it decreases with increasing of HXR energy,but with decreasing of MW frequencies;(3) The peak of higher energy channel is later than that of lower energy channel in HXR and γ-rays In contrast with this,the peak at higher frequency preceeds one at lower frequency in MW;(4) The profiles in MW peak appear later and decay is later than in HXR.For example,the peak at 35 GHz is delaied by 17s with respect to channel X₂₃ (54-100 keV),the everage delay at 35 GHz and at M₁₀ channel are well marched,which agrees with expectation of the turbulence acceleration theory;(5) Delay time increases with increasing of spike duration,chnnel energy,MW wavelength,and hardness of HXR spectrum;(6) During spike bursts the spectra of HXR exhibit soft-hard-soft behavior (varying amplitude being about 1),which means these spikes result from acceleration of electrons.The power-low spectrum index and the total numbers of nonthermal electrons in the HXR burst source are estimated on the assumption of thin target model.The magnetic field strength (being about 2.6×10^-3-3.0×10^-2T) in the MW radiation source is also estimated.