Short‐Lived Absorptive Type III–like Microwave Bursts as a Signature of Fragmented Electron Injections

Abstract

In this paper, we devote ourselves to interpreting the short-lived absorptive type IIIYlike microwave bursts in the 2006 December 13 flare event observed with high temporal and spectral resolutions (8 ms and 10 MHz) by the Chinese Solar Broadband Radio Spectrometer (SBRS/Huairou) at 2.6Y3.8 GHz. In the decimeter-centimeter wavelength range, we first present the observations of short-lived bursts represented as a number of absorptive ''spikes'' superposed on the type IV continuum that can be connected by fast-drifting lines. The mean drift rate, the instantaneous bandwidth, and the absorption depth of these absorptive spikes are about À12 GHz s À1 , 70 MHz, and 40%, respectively. The duration at a single frequency band can be less than the instrument resolution of 8 ms. On the basis of numerical investigations of the loss-cone instability, we suggest that fragmented electron injections with durations of as short as several milliseconds into the loss cone could be the most appropriate mechanism with which to explain the bursts. The length of an electron beam is estimated to be about 400 km, on the basis of the observational results. These injections may be related to the fragmented energy release processes during the flare. We also observe some absorptive type IIIYlike bursts accompanying ordinary type III bursts with reverse drifts. They start at the same frequency, and the starting frequency slowly drifts to the low-frequency region. This could be a signature of propagating bidirectional electron beams originating near the reconnection region.

Microwave Type Iii Pair Bursts in Solar Flares

“…(Tan et al 2007(Tan et al , 2010 constant of 2.90 GHz during the type III pairs. This train behaves as absorption structure which is analyzed by Chen & Yan (2008).…”

“…The RS branches start from 2.95 -2.92 GHz and extend to 3.3 -3.6 GHz with average frequency drift of about 8.6±0.8 GHz s −1 , the burst lifetime is 0.1 -0. constant of 2.90 GHz during the type III pairs. This train behaves as absorption structure which is analyzed by Chen & Yan (2008).…”

Complex Zebra Patterns in Solar Radio Emission and New Generation Mechanisms

“…The maximum absorptive effect occurred at the DPR levels. The parameters of millisecond spikes are determined by small dimensions of the particle beams and local scale heights in the radio source (as Chen and Yan [2008] showed).…”

Radio fine structures in dm–cm wavelength range associated with magnetic reconnection processes

“…Their observational parameters are about 20-60% in absorption depth, $12 GHz s À1 in frequency drift rate, with about 70 MHz instantaneous bandwidth and about 2.5% relative bandwidth. It is suggested that these short-lived absorptive type III-like microwave bursts may be due to fragmented electron injections under the interactions between emerging fluxes and the multiple flare loops, and bi-directional electron beams can be generated near the reconnection region (Chen and Yan, 2008). Some of these beams can propagate upward into the magnetic trap where the continuum emission forms, which then results in the observed absorptive type III-like bursts with negative drift rates.…”

“…The microwave observation shows that the mean frequency drift rate of these starting frequencies is around 60 MHz s À1 , which means that the reconnection region is moving upward, and its velocity can be estimated to be 400 km s À1 . It is natural to believe that such a phenomenon is due to the ascending motion of the emerging fluxes (Chen and Yan, 2008).…”