关于日冕双向电子束的加速问题

Acceleration of Bidirectional Eletron Beams in Corona

介绍了云南天文台和北京天文台频谱仪所观测到具有正、负频漂的米波Ⅲ型爆发和微波尖峰辐射。对双向电子束源的频率和高度进行了估计。 2个事件都表明在具有正、负频漂率的爆发之间有一分界频率 ( 2 50和 2 90 0MHz) ,这说明爆发源是一个复杂加速源 ,电子束同时向上、下 2个方向注入。由本文的 2个事例可以说明 :1 .双向电子束的转换 (changeover)范围是在 2 50～ 2 90 0MHz的宽频带里 ,并且起源是在很小范围 ( 4～ 70MHz)内。这些电子束从高层到低层日冕都有一个很窄的独立加速区 ,文中的Ⅲ型爆发对可能是它们的等离子体辐射现象。 2 .在低日冕分离开放磁场和闭合磁场的电流片 ,以及高日冕相反方向的开放磁力线的交叉区域可能都是双向电子加速区。从闭合磁场到开放磁场的磁拓扑范围将是很大的 (大约在光球上 2× 1 0 4km到 1 0 .7× 1 0 4km)。

The metric and microwave spike emission with negative and positive frequency drift rate observed with radio spectrometers at Yunnan and Beijing observatories are presented.The frequencies and heights at which the bidirectional electron beams originated are estimated.Two events reveal a separatrix frequency (at 250 and 2900 MHz) between normal-and reverse-drifting radio bursts,indicating a compact acceleration source where electron beams are injected in both the upward and downward directions.There cases may indicate that the change over frequencies of bidirectional electron beams are within a large band from 250 to 2900 MHz and the originating (frequency bands of separatrix) are in a very small (4 to 100 MHz) and different bands.The type Ⅲ bursts appear to be a plasma emission phenomenon from a beam of electrons which seem to have widely separated acceleration regions from the high to low corona.These cases suggests that current sheets that separate open and closed magnetic fluxes in the low corona,and oppositely directed open field lines in the high corona are possible sites for bidirectional electron acceleration.The regions of magnetic topology from closed to open magnetic field structures should be very large (about from 2×10 4km to 10.7×10 4km above the photosphere).