摘要
本文介绍了由捷克Ondˇrejov天文台观测到的 1 992年 8月 2 2日 1 2 :36 :2 6— 1 2 :36 :32UT发生的U型暴 ,U型暴的频率范围为 1 .0— 2 .8GHz,在国际上尚属首例 .从分析得到以下几点结论 :(1 )上下臂的频漂率分别为 1 .2 5和 0 .2 2 5GHz/s,其电子束流的速度分别为 0 .38c和 0 .2 6c ,它是由等离子体二次谐波发射造成的 .(2 )上升臂的爆发衰减时间常数大于下降臂的 .(3)频谱极大频率随时间变化呈现出从高频到低频再到高频的变化 .(4)上升臂的频宽大于下降臂的约一倍左右 ,这与上升臂频漂远大于下降臂的有关 .(5 )从频宽得到上、下臂的速度弥散分别为 (Δvv) a=0 .42和 (Δvv) d=0 .47.
This paper describes a type U burst occurring between 12:36:26-12:36:32 UT on 1992 August 22 as observed at 1.0-2.8 GHz from the Ondejov Observatory, Czech. To our knowledge this is the first example of a type U burst detected in the decimetric range. From analyzing we come to the following conclusion: 1. The frequency drift rates of the ascending and descending branches are 1.25 and 0.225 GHz/s, respectively, and the velocities of the electron beam are 0.38 c and 0.26 c, respectively, where c is the velocity of light in vacuum. 2. The time constant of burst decay on the ascending branch is greater than that on the descending branch. 3. The maximum frequencies of instantaneous spectra changed from the highest (1.92 GHz) to the lowest (1.0 GHz), then again toward a higher frequency (1.5 GHz). This is consistent with that predicted by the plasma emission theory. 4. The band widths of the ascending branch are about twice as those of the descending branch. This may be caused by the high drift rates of the ascending branch. 5. The velocity dispersions of the ascending and descending branches are estimated as ( Δ vv) a = 0.42 and ( Δ vv) d = 0.47 from the band widths of the bursts.
基金
国家自然科学基金!( 1 94 730 2 0 )
国家自然科学重大基金!(日地系统能量传输过程的研究 4 9391 4 0 0)资助课题
