Diagnosing the Source Region of a Solar Burst on 26 September 2011 by Microwave Type III Pairs

TL;DR

This study analyzes microwave type III pair bursts during a solar flare, diagnosing source region plasma parameters and electron energies to understand the microphysics of solar burst origins.

Contribution

It applies a recent diagnostic method to determine plasma conditions and electron energies in the source region of microwave type III bursts during a solar flare.

Findings

Plasma density, temperature, and magnetic field remain stable during burst trains.

Electron energy peaks align with hard X-ray emissions.

High plasma beta indicates a highly dynamic source region.

Abstract

This work reports a peculiar and interesting train of microwave type III pair bursts in the impulsive rising phase of a solar flare on 2011 September 26. The observations include radio spectrometers at frequency of 0.80 - 2.00 GHz, hard X-ray (RHESSI and FERMI), EUV images of SWAP/PROBA-2 and magnetogram of HMI/SDO. By using a recently developed method (Tan et al. 2016a), we diagnosed the plasma density, temperature, plasma beta, magnetic field near the source region, the energy of energetic electrons and the distance between the acceleration region and the emission start sites of type III bursts. From the diagnostics, we find that: (1) The plasma density, temperature, magnetic field, and the distance between the acceleration region and the emission start sites almost have no obvious variations during the period of type III pair trains, while the energy of electrons has an obvious peak value which is consistent to the hard X-ray emission. (2) The plasma beta is much higher than an unity showing a highly dynamic process near the emission start site of type III bursts. (3) Although the reversed-slope type III branches drift slower at one order of magnitude than that of the normal type III branches, the related downgoing and upgoing electrons still could have same order of magnitude of energy. These facts indicate that both of the upgoing and downgoing electrons are possibly accelerated by similar mechanism and in a small source region. This diagnostics can help us to understand the microphysics in the source region of solar bursts.