Detailed Thermal and Nonthermal Processes in an A-class Microflare

How microflares behave and differ from large flares is an important question in flare studies. Although they have been extensively investigated, microflares are not fully understood in terms of their detailed energy release processes and the role of energetic electrons. A recent study on an A-class microflare suggests the existence of a nonthermal component down to 6.5 keV, indicating that accelerated electrons play an important role in microflares, as in large flares. Here, we revisit this event, and present a comprehensive, quantitative analysis of the energy release and plasma heating processes. Using careful differential emission measure (DEM) analysis, we calculate the thermal X-ray fluxes. By subtracting this multithermal component from the observed data, we confirm the existence of the remaining nonthermal component. In addition, we analyze the clear evaporation process and report the first imaging evidence for a low-energy cutoff of energetic electrons in EM maps of >10 MK plasma, which first appeared as two coronal sources significantly above the chromospheric footpoints. Detailed calculations of electron transport, based on the electron parameters and the evolution of loop dynamics, provide strong evidence of a beam-driven plasma heating process with a low-energy cutoff consistent with that derived independently from DEM analysis. This study reveals the important role of electron thermalization and low-energy cutoffs in the physical processes of microflares.