Narrowband Spikes Observed During the 13 June 2012 Flare in the 800 – 2000 MHz Range

Abstract

Narrowband (∼5 MHz) and short-lived (∼0.01 s) spikes with three different distributions in the 800 – 2000 MHz radio spectrum of the 13 June 2012 flare are detected and analyzed. We designate them as SB (spikes distributed in a broad band or bands), SZ (spikes distributed in zebra-like bands) and SBN (spikes distributed in broad and narrow bands). On analyzing AIA/SDO images of the active region NOAA 11504, a rough correspondence between groups of the spikes observed at 1000 MHz and peaks in the time profiles of AIA channels taken from the flare subarea close to the leading sunspot is found. Among the types of spikes the SZ type is the most interesting because it resembles zebras. Therefore, using autocorrelation and crosscorrelation methods we compare SZ and SBN spikes with the typical zebra observed in the same frequency range. While the ratio of SZ band frequencies with their frequency separation (220 MHz) is about 4, 5, and 6, in the zebra the frequency stripe separation is about 24 MHz and the ratio is around 50. Moreover, the bandwidth of SZ bands, which consists of clouds of narrowband spikes, is much broader than that of zebra stripes. This comparison indicates that SZ spikes are generated in a different way from the zebra, but in a similar way to SBN spikes. We successfully fit the SZ band frequencies by the Bernstein modes. Based on this fitting we interpret SZ and SBN spikes as those generated in the model of Bernstein modes. Thus, the magnetic field and plasma density in the SZ spike source are estimated to be about 79 G and 8.4 × 10⁹ cm⁻³, respectively.