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NuSTAR Observation of Energy Release in 11 Solar Microflares

Duncan, Jessie and Glesener, Lindsay and Grefenstette, Brian W. and Vievering, Juliana and Hannah, Iain G. and Smith, David M. and Krucker, Säm and White, Stephen M. and Hudson, Hugh (2021) NuSTAR Observation of Energy Release in 11 Solar Microflares. Astrophysical Journal, 908 (1). Art. No. 29. ISSN 1538-4357. doi:10.3847/1538-4357/abca3d.

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Solar flares are explosive releases of magnetic energy. Hard X-ray (HXR) flare emission originates from both hot (millions of Kelvin) plasma and nonthermal accelerated particles, giving insight into flare energy release. The Nuclear Spectroscopic Telescope ARray (NuSTAR) utilizes direct-focusing optics to attain much higher sensitivity in the HXR range than that of previous indirect imagers. This paper presents 11 NuSTAR microflares from two active regions (AR 12671 on 2017 August 21 and AR 12712 on 2018 May 29). The temporal, spatial, and energetic properties of each are discussed in context with previously published HXR brightenings. They are seen to display several "large flare" properties, such as impulsive time profiles and earlier peak times in higher-energy HXRs. For two events where the active region background could be removed, microflare emission did not display spatial complexity; differing NuSTAR energy ranges had equivalent emission centroids. Finally, spectral fitting showed a high-energy excess over a single thermal model in all events. This excess was consistent with additional higher-temperature plasma volumes in 10/11 microflares and only with an accelerated particle distribution in the last. Previous NuSTAR studies focused on one or a few microflares at a time, making this the first to collectively examine a sizable number of events. Additionally, this paper introduces an observed variation in the NuSTAR gain unique to the extremely low livetime (<1%) regime and establishes a correction method to be used in future NuSTAR solar spectral analysis.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Duncan, Jessie0000-0002-6872-4406
Glesener, Lindsay0000-0001-7092-2703
Grefenstette, Brian W.0000-0002-1984-2932
Vievering, Juliana0000-0002-7407-6740
Hannah, Iain G.0000-0003-1193-8603
Smith, David M.0000-0002-0542-5759
Krucker, Säm0000-0002-2002-9180
White, Stephen M.0000-0002-8574-8629
Hudson, Hugh0000-0001-5685-1283
Alternate Title:NuSTAR Observation of Energy Release in Eleven Solar Microflares
Additional Information:© 2021 The American Astronomical Society. Received 2020 August 28; revised 2020 October 22; accepted 2020 November 11; published 2021 February 9. This work was supported under an NSF Faculty Development Grant (AGS-1429512) to the University of Minnesota, the 2019 NASA Fellowship Program (80NSSC19k1687), an NSF CAREER award (NSF-AGS-1752268), the SolFER DRIVE center (80NSSC20K0627), and the NASA NuSTAR Guest Observer program (80NSSC18K1744). I.G.H is supported by a Royal Society University Fellowship. The authors also wish to thank Pascal Saint-Hilaire for help with eclipse predictions in planning the 2017 August 21 NuSTAR observation.
Group:NuSTAR, Space Radiation Laboratory
Funding AgencyGrant Number
NASA Postdoctoral Program80NSSC19K1687
Subject Keywords:The Sun; Solar flare spectra; Solar x-ray flares; Non-thermal radiation sources; Solar flares; Solar physics
Issue or Number:1
Classification Code:Unified Astronomy Thesaurus concepts: The Sun (1693); Solar flare spectra (1982); Solar x-ray flares (1816); Non-thermal radiation sources (1119); Solar flares (1496); Solar physics (1476)
Record Number:CaltechAUTHORS:20210205-093239844
Persistent URL:
Official Citation:Jessie Duncan et al 2021 ApJ 908 29
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:107934
Deposited By: George Porter
Deposited On:05 Feb 2021 22:54
Last Modified:16 Nov 2021 19:07

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