FOXSI-2 Solar Microflares: Hard X-ray Spectroscopy and Multi-instrument Differential Emission Measure Analysis

Sensitive measurements of solar flares in the hard X-ray regime are necessary for investigating energy release and transfer during flaring events, as hard X-rays provide insight into the acceleration of electrons and emission of high-temperature plasmas. The Focusing Optics X-ray Solar Imager (FOXSI), a hard X-ray instrument flown on three sounding rocket campaigns, offers improved capabilities compared to previous indirect imagers by using focusing optics for solar observations in the 4-20 keV range. During the second flight, which occurred on 2014 December 11, FOXSI-2 observed two microflares, estimated as GOES class A0.1 and A0.3. Here we present imaging and spectral analyses of these microflares, investigating the nature of energy release and exploring the structure and dynamics in comparison to larger flares. Additionally, using coordinated observations during the FOXSI-2 flight from Hinode/XRT and SDO/AIA in soft X-rays and extreme ultraviolet, respectively, we present a multi-instrument differential emission measure analysis with unprecedented temperature coverage for characterizing solar microflares. With this unique data set, we measure faint emission from high-temperature plasma (>5 MK) and find evidence of spatial and temporal complexity for small-scale solar events.