Microwave type III bursts and pulsation groups

• Published in: Astronomy and astrophysics (Berlin) 2005-07, Vol.437 (2), p.691-697
• Main Authors: Ning, Z., Ding, M. D., Wu, H. A., Xu, F. Y., Meng, X.
• Format: Article
• Language: English
• Subjects: Sun: radio radiation
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361:20041944

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 $2.0 \pm 0.6$ 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 $3.7 \pm 1.1$ 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.