Quasi-periodic Pulsations before and during a Solar Flare in AR 12242

• Published in: The Astrophysical journal Vol. 878; no. 2; pp. 78 - 89
• Main Authors: Chen, Xingyao, Yan, Yihua, Tan, Baolin, Huang, Jing, Wang, Wei, Chen, Linjie, Zhang, Yin, Tan, Chengming, Liu, Donghao, Masuda, Satoshi
• Format: Journal Article
• Language: English
• Published: Philadelphia The American Astronomical Society 20.06.2019; IOP Publishing
• Subjects: Astrophysics; Coronal loops; Plasmas (physics); Radio imagery; Solar flares; Sun: flares; Sun: oscillations; Sun: radio radiation; Sunspots
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/ab1d64

Quasi-periodic pulsations (QPPs) are frequently observed in solar flares, which may reveal some essential characteristics of both thermal and nonthermal energy releases. This work presents multi-wavelength imaging observations of an M8.7 flare in active region AR 12242 on 2014 December 17. We found that there were three different QPPs: UV QPPs with a period of about 4 minutes at 1600 images near the center of the active region lasting from the preflare phase to the impulsive phase; EUV QPPs with a period of about 3 minutes along the circular ribbon during the preflare phase; and radio QPPs with a period of about 2 minutes at frequencies of 1.2-2.0 GHz around the flaring source region during the impulsive phase. The observations include the radio images observed by the Mingantu Spectral Radioheliograph in China at frequencies of 1.2-2.0 GHz for the first time, microwave images by the Nobeyama Radioheliograph, UV and EUV images by AIA/SDO, and a magnetogram by HMI/SDO. We suggest that the 4 minute UV QPPs should be modulated by the sunspot oscillations, and the 3 minute EUV QPPs are closely related to the 2 minute radio QPPs for their source regions connected by a group of coronal loops. We propose that the intermittent magnetic reconnecting downward and upward plasmoids may be the possible trigger of both the preflare 3 minute EUV QPPs and the impulsive 2 minute radio QPPs. The other possible mechanism is LRC oscillation, which is associated with the current-carrying coronal loops. The latter mechanism implies that the existence of preflare QPPs may be a possible precursor to solar flares.