Multiple electron acceleration instances during a series of solar microflares observed simultaneously at X-rays and microwaves

TL;DR

This study combines X-ray and radio observations to reveal multiple, spatially distinct electron acceleration sites during small solar microflares, highlighting the complexity and frequency of particle acceleration in active regions.

Contribution

It demonstrates that particle acceleration occurs frequently at multiple locations within active regions, using high-sensitivity radio observations alongside X-ray data.

Findings

Multiple acceleration sites identified within active regions.

Electron acceleration occurs frequently and at various locations.

Some radio emissions are unrelated to the main flare site.

Abstract

Even small solar flares can display a surprising level of complexity regarding their morphology and temporal evolution. Many of their properties, such as energy release and electron acceleration can be studied using highly complementary observations at X-ray and radio wavelengths. We present X-ray observations from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and radio observations from the Karl G. Jansky Very Large Array (VLA) of a series of GOES A3.4 to B1.6 class flares observed on 2013 April 23. The flares, as seen in X-ray and extreme ultraviolet (EUV), originated from multiple locations within active region NOAA 11726. A veritable zoo of different radio emissions between 1 GHz and 2 GHz was observed co-temporally with the X-ray flares. In addition to broad-band continuum emission, broad-band short-lived bursts and narrow-band spikes, indicative of accelerated electrons, were observed. However, these sources were located up to 150 arcsec away from the flaring X-ray sources but only some of these emissions could be explained as signatures of electrons that were accelerated near the main flare site. For other sources, no obvious magnetic connection to the main flare site could be found. These emissions likely originate from secondary acceleration sites triggered by the flare, but may be due to reconnection and acceleration completely unrelated to the co-temporally observed flare. Thanks to the extremely high sensitivity of the VLA, not achieved with current X-ray instrumentation, it is shown that particle acceleration happens frequently and at multiple locations within a flaring active region.