FOXSI-2 Solar Microflares. I. Multi-instrument Differential Emission Measure Analysis and Thermal Energies

P. S. Athiray, Juliana Vievering, Lindsay Glesener, Shin Nosuke Ishikawa, Noriyuki Narukage, Juan Camilo Buitrago-Casas, Sophie Musset, Andrew Inglis, Steven Christe, S. m. Krucker, Daniel Ryan

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4 Scopus citations

Abstract

In this paper we present the differential emission measures (DEMs) of two sub-A class microflares observed in hard X-rays (HXRs) by the FOXSI-2 sounding rocket experiment, on 2014 December 11. The second Focusing Optics X-ray Solar Imager (FOXSI) flight was coordinated with instruments X-ray Telescope (Hinode/XRT) and Solar Dynamics Observatory/Atmospheric Imaging Assembly (AIA), which provided observations in soft X-rays and Extreme Ultraviolet. This unique data set offers an unprecedented temperature coverage, useful for characterizing the plasma temperature distribution of microflares. By combining data from FOXSI-2, XRT, and AIA, we determined a well-constrained DEM for the microflares. The resulting DEMs peak around 3 MK and extend beyond 10 MK. The emission measures determined from FOXSI-2 were lower than 1026 cm-5 for temperatures higher than 5 MK; faint emission in this range is best measured in HXRs. The coordinated FOXSI-2 observations produce one of the few definitive measurements of the distribution and the amount of plasma above 5 MK in microflares. We utilize the multi-thermal DEMs to calculate the amount of thermal energy released during both the microflares as ∼5.0 × 1028 erg for Microflare 1 and ∼1.6 × 1028 erg for Microflare 2. We also show the multi-thermal DEMs provide more comprehensive thermal energy estimates than isothermal approximation, which systematically underestimates the amount of thermal energy released.

Original languageEnglish (US)
Article number78
JournalAstrophysical Journal
Volume891
Issue number1
DOIs
StatePublished - Mar 1 2020

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