Drifting bands of solar radio spikes

The solar flare (1N/C5.3) occurred in NOAA 8742 on October 27, 1999, and the accompanied complex radio burst was observed by the spectrometer with both high temporal (5 ms) and frequency (10 MHz) resolutions at Purple Mountain Observatory (PMO). It started at 04:27:42 UT, peaked at 04:28:42 UT and ended at 04:29:18 UT. The most significant feature of the event might be the sequential spikes in both time and frequency to form three slow drift bands over the frequency range of ～5 to 7.5 GHz with almost the same drift rate about 2.7 GHz/s. The relative bandwidth for the individual spikes varied from 1.6% to 4.9%, typically 3.3%. Based on electron cyclotron maser action driven by loss-cone anisotropy, the rare phenomena of slow drift band consisting of spikes were interpreted by spike source moving back and forth along the magnetic loop. Also, the estimations of the narrow bandwidths of spike given by electron cyclotron maser theory coincided well with the observations. Supported by the National Natural Science Foundation of China (Grant Nos. 10333030 and 10273025)