Table 1. Standard specifications of groups of spikes throughout the flare in Figure 1: Times, frequency variety, types, maximal variety of frequency bands (MNFB), and characteristic ratios of neighboring bands of spikes (BR).
Figure 1. The radio spectrum observed at 13:10:00– 13:30:00 UT during the 13 June 2012 flare by the Ondřejov radiospectrograph.
The solar radio spikes can supply detailed information about plasma procedures in solar flares on kinetic scales. Amongst them, the decimetric spikes belong to the most fascinating ones due to the fact that they are recorded sometimes near to the starting frequency of Type-III bursts and in relation to tough X-ray emissions.
Stepanov et al. (1999) and Bárta and Karlický (2001) presented designs where spike frequencies correspond to those of the upper-hybrid waves, and Willes and Robinson (1996) presented the design with spike frequencies representing the Bernstein modes. Luo et al. (2021) proposed that spikes are created at the termination shock formed above the flare game, where a diffuse supraarcade fan and wide varieties of plasma downflows exist. This analysis is close to the concept that the narrowband dm spikes are generated by superthermal electrons in the magnetohydrodynamic turbulence in the magnetic reconnection outflows (Karlický, Sobotka, and Jiřička,1996).
There is an important additional element of the narrowband dm spikes that is not frequently thought about in theoretical models. Namely, spikes appear in frequency bands and the ratio of band frequencies is noninteger (1.06– 1.54) (Krucker and Benz 1994). In the paper by Karlický, Benáček, and Rybák (2021 ), this result was not only validated, but extremely narrow bands of spikes in the 7 November 2013 event allowed a successful fit of the band frequencies by the Bernstein modes.
We examined spike occasions observed during the 13 June 2012 flare by 800-2000 MHz Ondřejov radiospectrograph with a time resolution 0.01 s and frequency resolution 4.7 MHz. We analyzed the relation in between the radio and AIA/SDO UV, HMI/SDO, and RHESSI X-ray.
The radiospectrogram is shown in Figure 1, and the numbered spike occasions are classified in Table 1 into three categories according to their look in the radio spectrum: spikes distributed in a broad band or bands (SB), surges distributed in zebra-like bands (SZ), and spikes dispersed in narrow and broad bands (SBN). If more than one band appears, characteristic ratios of neighboring spikes are determined. Examples of spike types are displayed in Figure 2.
Figure 2. Spikes observed during the 13 June 2012 flare. The radio spectrum reveals spikes distributed in a) broad band or bands (SB), b) zebra-like bands (SZ), and c) in narrow and broad bands (SBN).
We validate that the dm spikes are observed mostly throughout the spontaneous flare phase. We tried to browse for some relation in between spikes groups and variations of intensities in selected flare areas utilizing AIA/SDO observations. We discovered interesting relation for AIA intensities taken from one end of the sigmoidal flare structure where many magnetic-field lines of flare loops were focused.
We found that similar autocorrelations of SZ and SBN favor the very same generation mechanism of these spikes. Due to the fact that of its resemblance to Karlický et al. (2021 ), we analyze SZ and SBN as created in Bernstein modes. We supported this interpretation by simulations of Bernstein modes.
We compared the SZ type and a zebra observed on 1 August 2010 in the same frequency variety. We found a couple of differences:
Stepanov et al. (1999) and Bárta and Karlický (2001) provided designs where spike frequencies correspond to those of the upper-hybrid waves, and Willes and Robinson (1996) presented the design with spike frequencies corresponding to the Bernstein modes. Luo et al. (2021) proposed that spikes are produced at the termination shock formed above the flare arcade, where a scattered supraarcade fan and plethoras of plasma downflows are present. In the paper by Karlický, Benáček, and Rybák (2021 ), this result was not only validated, however extremely narrow bands of spikes in the 7 November 2013 occasion made it possible for a successful fit of the band frequencies by the Bernstein modes.
The radiospectrogram is shown in Figure 1, and the numbered spike events are categorized in Table 1 into 3 categories according to their appearance in the radio spectrum: spikes distributed in a broad band or bands (SB), surges distributed in zebra-like bands (SZ), and spikes distributed in broad and narrow bands (SBN). Characteristic ratios of neighboring spikes are identified if more than one band appears.
Separation frequency has to do with 220 MHz in the SZ case, while around 24 MHz in zebras,
The autocorrelation variability in time is significantly higher for zebras than for SZ type,
The ratios in between SZ spike bands is (4.4, 5.1, 6.0, 7.0) and (4.0,4.9, 6.0), while for zebras is ~ 52,.
The separation frequency of surrounding zebra stripes changes in different methods for different sets. This behavior omits the possibility that zebras are created in one emission source, as are the SZ type spikes by Bernstein modes.
In accordance with our previous ideas (Bárta and Karlický, 2001), we conclude that the SZ and SBN are formed in an area of magnetic reconnection outflow, where the plasma is in a turbulent state. $, respectively.
Based on current paper by Karlicky et al., Narrowband spikes observed throughout the 13 June 2012 flare in the 800-2000 MHz range, Solar Physics 297:54 (2022 ), DOI: https://doi.org/10.1007/s11207-022-01989-4.
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