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The narrow-band spikes observed by Marian Karliki et al. during the 2012 June 13 flare in the 800–2000 MHz band – European Solar Radio Astronomer Community

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Solar radio spikes can provide detailed information on plasma processes in solar flares on kinetic scales. Among them, decimetric bursts are among the most interesting, because in some cases they are recorded close to the initial frequency of type III bursts and are associated with hard X-ray emission.

Stepanov and others. (1999) and Barth and Karlitsky (2001) models are presented in which the burst frequencies correspond to the frequencies of the upper hybrid waves, and Wills and Robinson (1996) presented a model with burst frequencies corresponding to Bernstein modes. Luo and others. (2021) suggested that flares occur at the termination of a shock that forms above the flare arcade, where a diffuse supraorbital fan and multiple downdrafts of plasma are present. This interpretation is close to the idea that narrowband dm junctions are generated by superthermal electrons in magnetohydrodynamic turbulence in magnetic reconnection flows (Karlicki, Sobotka and Jirzhichka, 1996).

There is an important additional aspect of narrowband dm spikes that is not often considered in theoretical models. Namely, spikes appear in frequency ranges, and the frequency ratio of the range is non-integer (1.06 – 1.54) (Crooker and Benz 1994). In the article a Karlicki, Benacek and Rybak (2021), this result was not only confirmed, but the very narrow burst bands in the November 7, 2013 event made it possible to successfully fit the frequency bands with Bernstein modes.

Observations

We investigated the peak events observed during the 2012 June 13 flare on the 800–2000 MHz Ondzeev radio spectrograph with a time resolution of 0.01 s and a frequency resolution of 4.7 MHz. In addition, we analyzed the connection between the radio and X-ray emission of AIA/SDO UV, HMI/SDO, and RHESSI.

The radio spectrogram is shown in Figure 1, and the numbered bursts are classified in Table 1 into three categories based on their appearance in the radio spectrum: bursts distributed in a broad band or bands (SB), bursts distributed in zebra stripes (SZ), and spikes , distributed in wide and narrow bands (SBN). The characteristic ratio of adjacent spikes is determined when more than one band appears. Examples of spike types are shown in Figure 2.

Figure 1. Radio spectrum observed at 13:10:00 – 13:30:00 UT during the 13 June 2012 flare at the Ondřejov radio spectrograph.

Table 1. Main parameters of spike groups during the burst in Figure 1: timing, frequency range, types, maximum number of frequency bands (MNFB), and characteristic ratio of neighboring spike bands (BR).

Figure 2. Spikes observed during the 2012 June 13 flare.The radio spectrum shows spikes distributed in a) a broad band or bands (SB), b) zebra-like bands (SZ), and c) broad and narrow bands (SBN).

Conclusions

We confirm that dm bursts are observed mainly during the pulse phase of the flare. We attempted to find some relationship between peak groups and intensity variations at selected flare locations using AIA/SDO observations. We found an interesting relation for the AIA intensity taken from one end of the flare’s sigmoid structure, where many of the flare’s magnetic field lines are concentrated.

We found similar autocorrelations SZ and SBN advocate the same mechanism for the generation of these spikes. Because of its similarity to Karlitsky and others. (2021)interpret SZ and SBN generated in Bernstein modes. We supported this interpretation by simulating Bernstein modes.

We compared SZ type and zebra was observed on August 1, 2010 in the same frequency range. We found a few differences:

  • The separation frequency is about 220 MHz in the case of SZ, while it is about 24 MHz in the zebra,
  • The autocorrelation variability over time is much higher for zebras than for the SZ type,
  • The ratios of SZ spike bands are (4.4, 5.1, 6.0, 7.0) and (4.0, 4.9, 6.0) and for zebras ~52,
  • The frequency of separation of adjacent zebra stripes varies differently for different pairs. Such behavior excludes the possibility that zebras originate from a single emission source, as SZ-type spikes by Bernstein modes.

In accordance with our previous ideas (Barta and Karlitsky, 2001)we conclude that SZ and SBN are formed in c in the outflow region of the magnetic reconnection, where the plasma is in a turbulent state. Using the Bernstein model, we estimated the mean magnetic field strength and plasma density in the SZ source to be approximately 79 G and $8.4times 10^9$ cm$^{−3}$ , respectively.

Based on recent work by Karlicky et al.,’Narrowband bursts were observed in the 800-2000 MHz band during the 13 June 2012 flare‘, Solar Physics 297:54 (2022), DOI: https://doi.org/10.1007/s11207-022-01989-4

Links

Barta, M. and Karlitsky, M. 2001, A&A, 379, p. 1045–1051.

Karlitsky, M., Sobotka, M., and Jirzhichka, K. 1996, Sol. Phys., 168, 2.

Karlitsky M., Benacek J. and Rybak J. 2021, ApJ, 910, 2.

Crooker S. and Benz AA. 1994, A&A, 285, p. 1038–1046.

Luo, Y., Chen, B., Yu, S., Bastian, et al. 2021, ApJ, 911, 1.

Stepanov A.V., Kliem B., Kruger A. and others. 1999, ApJ, 524, 2.

Wills, AJ and Robinson, PA 1996, ApJ, 467, 465.

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