MUSER Observations of an M8.7 Flare Event on 2014 December 17
Yihua Yan, CAS Key Laboratory of Solar Activity, National Astronomical Observatories, Chinese Academy ofSciences
The solar radio bursts are strongly related to solar activities. We present the solar radio bursts observed by the Mingantu Spectral Radioheliograph (MUSER) in China with 25 ms cadence and 25 MHz spectral resolution at 0.4-2.0 GHz and other multi-wavelengths imaging observations of an M8.7 flare/CME event in a circular active region on 2014 December 17. The solar radio spectral observations show quasi-periodic pulsations overlaid on a type IV radio continuum, which present oscillations of the non-thermal emission at a period of about 2 minutes during the flaring impulsive phase. The imaging observations show that the radio bursts cover above a region with positive magnetic field in the middle of this active region. Additionally, the modelling extrapolation shows that there are three magnetic topological structures with different scales of lengths, which coincide with the EUV imaging observations. We also find that the circular ribbon is brightening, expanding and oscillating at a period of about 3 minutes during the preflare phase. The above associated spatial locations suggest that the EUV oscillations during preflare phase are possibly related to the radio oscillations during the flaring impulsive phase. Those results also suggest that the null-point reconnection may happen before the flare onset and the preflare oscillations may play an important role in triggering the following solar flare.