Microwave type III bursts and pulsation groups

¹ Department of Astronomy, Nanjing University, Nanjing 210093, PR China e-mail: ningzongjun@hotmail.com
² Purple Mountain Observatory, Nanjing 210093, PR China

Received: 3 September 2004
Accepted: 8 March 2005

Abstract

We analyse 22 continuous microwave reverse slope (RS) type III and 21 microwave pulsation groups observed by the Purple Mountain Observatory (PMO) spectrometer over the frequency range of 4.5-7.5 GHz from 1999-2003. The RS type III groups have an average of 12 bursts per group, a mean duration of 0.1-2 s around 6 GHz, a mean quasi-period of  s and a mean drift rate of 7.0 GHz s^-1. The shortest quasi-period is measurable down to 0.05 s thanks to the high time resolution of this instrument. The microwave pulsation groups have an average of 22 events per group, a mean duration of 3-4 s and a mean quasi-period of  s. The RS type III bursts have the same quasi-period as the upward type III bursts documented before. We discuss two possible origins of the quasi-periodicity of type III bursts. One is the quasi-periodic process in magnetic reconnection at the same site, and the other is spatially unresolved stochastic processes in solar flares.