Oscillations in the 45 – 5000 MHz Radio Spectrum of the 18 April 2014 Flare
Using a new type of oscillation map, made from the radio spectra by the wavelet technique, we study the 18 April 2014 M7.3 flare (SOL2014-04-18T13:03:00L245C017). We find a quasi-periodic character of this flare with periods in the range 65 – 115 seconds. At the very beginning of this flare, in connection with the drifting pulsation structure (plasmoid ejection), we find that the 65 – 115 s oscillation phase slowly drifts towards lower frequencies, which indicates an upward propagating wave initiated at the start of the magnetic reconnection. Many periods (1 – 200 seconds) are found in the drifting pulsation structure, which documents multi-scale and multi-periodic processes. On this drifting structure, fiber bursts with a characteristic period of about one second are superimposed, whose frequency drift is similar to that of the drifting 65 – 115 s oscillation phase. We also checked periods found in this flare by the EUV Imaging Spectrometer (EIS)/Hinode and Interface Region Imaging Spectrograph (IRIS) observations. We recognize the type III bursts (electron beams) as proposed, but their time coincidence with the EIS and IRIS peaks is not very good. The reason probably is that the radio spectrum is a whole-disk record consisting of all bursts from any location, while the EIS and IRIS peaks are emitted only from locations of slits in the EIS and IRIS observations.
KeywordsSun: flares Sun: radio radiation Sun: oscillations
This research was supported by Grants 16-13277S and 17-16447S of the Grant Agency of the Czech Republic. This work was supported by the Science Grant Agency project VEGA 2/0004/16 (Slovakia). Help of the Bilateral Mobility Project SAV-16-03 of the SAS and CAS is acknowledged. This article was created by the realization of the project ITMS No. 26220120029, based on the supporting operational Research and development program financed from the European Regional Development Fund. The authors are indebted to the Institute for Astronomy, ETH Zurich, and FHNW Windisch (Switzerland) and to the School of Physics and Astronomy of the University of Glasgow (Scotland, UK) for the Callisto data. This research has made use of NASA’s Astrophysics Data System. The wavelet analysis was performed with software based on tools provided by C. Torrence and G.P. Compo at http://paos.colorado.edu/research/wavelets .
Disclosure of Potential Conflicts of Interest
The authors declare that they have no conflicts of interest.
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