微波Ⅲ型爆发的观测特征

Observational Characteristics of Microwave Type III Bursts

统计分析了国家天文台2．6-3．8 GHz高时间分辨率射电动态频谱仪在23周峰年期间(1998．4—2003．1)观测到的266个III型爆发．对这些事件的频率漂移、持续时间、偏振、带宽、开始和结束频率做了详细分析．开始和结束频率的统计分析表明,开始频率在一个非常大的范围,从小于2．6 GHz到大于3．8 GHz,而结束频率的截止区相对集中,从2．82-3．76 G．Hz．这些现象说明,电子加速的高度相当分散,在观测频率范围内具有正、负漂移率的III型爆发数基本相等,这可能意味着被加速的向上和向下传播的电子束在2．6—3．8 GHz范围有相同的比例．统计结果表明,微波III型爆发的辐射机制主要是等离子体辐射和电子回旋脉泽辐射过程．

Type Ⅲ bursts 266 in total observed with the 2.6-3.8GHz high temporal resolution dynamic spectrometer of NAOC during the 23 rd solar cycle （from April 1998 to January 2003） are statistically analyzed. The frequency drift rates （normal and reverse slop）, durations, polarizations, bandwidth, starting and ending frequencies are analyzed in detail. From the statistical results of starting and ending frequencies it is shown that the range of starting frequencies is very large from less than 2.6GHz to greater than 3.8 GHz; but the ending frequency range is relatively narrow from 2.82 GHz to 3.76 GHz. These phenomena mean that the sites of electrons acceleration are quite scattered, while the cutoff regions of the radio type Ⅲ bursts are in the limiting domain. The burst number with positive and negative drift rates are nearly equal. This correlation may suggest the same proportion of electron beams in the directions of upward and downward, accelerated in the range of 2.6-3.8 GHz. The emission mechanisms of microwave type Ⅲ bursts are mainly caused by the plasma radiation and electron gyro-maser radiation. Usually, there are two excitements to produce type Ⅲ bursts： electron beam-drive and loss cone-drive type Ⅲ bursts. Their magnetic configurations mainly contain two types： opening or closed magnetic structures.