Frequency Distributions of Microwave Pulses for the 18 March 2003 Solar Flare

We analyze the pulses in high-frequency drift radio structures observed by the spectrometer at Purple Mountain Observatory (PMO) over the frequency range of 4.5 – 7.5 GHz during the 18 March 2003 solar flare. A number of individual pulses are determined from the drifting radio structures after the detected gradual component subtraction. The frequency distributions of microwave pulse occurrence as functions of peak flux, duration, bandwidth, and time interval between two adjacent pulses exhibit a power-law behavior, i.e. . From regression fitting in log-log space, we obtain the power-law indexes, α _P=7.38±0.40 for the peak flux, α _D=5.39±0.86 for the duration, and α _B=6.35±0.56 for the bandwidth. We find that the frequency distribution for the time interval displays a broken power law. The break occurs at about 500 ms, and their indexes are α _W1=1.56±0.08 and α _W2=3.19±0.12, respectively. Our results are consistent with the previous findings of hard X-ray pulses, type III bursts, and decimetric millisecond spikes.