Fine structures in ECM microwave oscillations

In solar flares, particles get accelerated to semi-relativistic/relativistic energies, which usually produce bright radio emission as bursts. Generally, radio bursts’ intensity depends on the emission mechanism and other factors like local magnetic fields, electron densities etc., of the magnetic loop. However, the effects like the presence of MHD waves in the loop and oscillatory reconnection can periodically change the local magnetic fields, i.e., producing the radio burst modulations/oscillations.

We examine pulsations in microwaves that occurred post GOES C1.5-class flare using Karl G. Jansky Very Large Array (VLA) at 1–2 GHz. VLA’s high temporal resolution (50 ms), along with imaging spectroscopy, provides a detailed view of pulsations. We also utilise the Solar Dynamics Observatory in extreme ultraviolet (EUV) and magnetic extrapolation to build a coherent picture. High brightness temperature (10⁸ MK), polarisation properties accompanied by suitable magnetic field strengths, and coronal density suggest Electron-Cyclotron Emission (ECM). The microwave pulsations observed from 1 GHz to 1.5 GHz exhibit a 4.5 sec period for all frequency channels. However, the intensity of the pulsation is higher at low frequencies. The imaging shows multiple source locations within a pulse at low frequencies. The magnetic extrapolation reveals the magnetic connectivity from the EUV flare footpoints to the microwave sources providing magnetic channels for the energetic particles from the flare site to the radio source location. I will discuss the detailed results and physical interpretation of the microwave pulsations seen for the event.