日冕分米波射电甚短周期脉动的观测证据

The Observational Evidence of Solar Coronal Decimetric Radio Pulsations With Very Short Periods

利用国家天文台云南天文台“分米波(700—1500 MHz)射电频谱仪”和“四波段太阳射电高时间分辨率同步观测系统”分别于2001年6月24日和1990年7月30日观测到了两个稀少事件,前者是一个小射电爆发,其上升相伴随有短周期(约29、40和100毫秒)的脉动,后者是一个射电大爆发,在2840 MHz上产生了周期约30毫秒的射电脉动。还着重讨论其甚短周期(如29—40毫秒)的脉动现象,甚短周期脉动可能是归因干起源在日冕深处不稳定区域的哨声波束周期链对射电辐射的凋制,或沉降电子束驱动的静电高混杂波,经由波-波非线性相互作用导致甚短周期的射电脉动。

Two rare events were observed with the decimetric (700-1500MHz) radio spectrometer and the synchronous observational system with high temporal resolution at four frequencies (1420, 2130, 2840, and 4260MHz) at Yunnan Observatory, National Astronomical Observatories of China on June 24, 2001 and July 30, 1990, respectively. The former is a small radio burst, associated with the pulsations with short periods (about 30, 40, and 100 milliseconds) in impulsive phase. The latter is a great radio burst, with the periods of the order of 30 milliseconds at 2840MHz. In this paper, the pulsations with very short periods of the order of 29-40 milliseconds are mainly emphasized and discussed. Such radio emission pulsations with very short periods may be generated by the modulation of the periodic trains of whistler packets originating in unstable region in the corona. Alternatively, these pulsations may be attributed to the wave-wave nonlinear interactions when a beam of precipitating electrons in a flaring loop drives electrostatic upper hybrid waves. These electrostatic waves can interact coherently with each other via the nonlinear oscillations to produce electromagnetic radiation with the periods of about 30 milliseconds at twice upper hybrid frequency.