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NuSTAR Observation of a Minuscule Microflare in a Solar Active Region

Cooper, Kristopher and Hannah, Iain G. and Grefenstette, Brian W. and Glesener, Lindsay and Krucker, Säm and Hudson, Hugh S. and White, Stephen M. and Smith, David M. (2020) NuSTAR Observation of a Minuscule Microflare in a Solar Active Region. Astrophysical Journal Letters, 893 (2). Art. No. L40. ISSN 2041-8213. PMCID PMC8780508. doi:10.3847/2041-8213/ab873e.

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We present X-ray imaging spectroscopy of one of the weakest active region (AR) microflares ever studied. The microflare occurred at ~11:04 UT on 2018 September 9 and we studied it using the Nuclear Spectroscopic Telescope ARray (NuSTAR) and the Solar Dynamic Observatory's Atmospheric Imaging Assembly (SDO/AIA). The microflare is observed clearly in 2.5–7 keV with NuSTAR and in Fe XVIII emission derived from the hotter component of the 94 Å SDO/AIA channel. We estimate the event to be three orders of magnitude lower than a GOES A class microflare with an energy of 1.1 × 10²⁶ erg. It reaches temperatures of 6.7 MK with an emission measure of 8.0 × 10⁴³ cm⁻³. Non-thermal emission is not detected but we instead determine upper limits to such emission. We present the lowest thermal energy estimate for an AR microflare in literature, which is at the lower limits of what is still considered an X-ray microflare.

Item Type:Article
Related URLs:
URLURL TypeDescription CentralArticle Paper
Cooper, Kristopher0000-0001-8589-3378
Hannah, Iain G.0000-0003-1193-8603
Grefenstette, Brian W.0000-0002-1984-2932
Glesener, Lindsay0000-0001-7092-2703
Krucker, Säm0000-0002-2002-9180
Hudson, Hugh S.0000-0001-5685-1283
White, Stephen M.0000-0002-8574-8629
Smith, David M.0000-0002-0542-5759
Additional Information:© 2020 The American Astronomical Society. Received 2020 March 17; revised 2020 April 4; accepted 2020 April 7; published 2020 April 22. This Letter made use of data from the NuSTAR mission, a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, funded by the National Aeronautics and Space Administration. These observations were supported through the NuSTAR Guest Observer program (NASA grant 80NSSC18K1744). This research has made use of SunPy v1.0.6, an open-source and free community-developed solar data analysis Python package (SunPy Community et al. 2015). This research also made use of HEASoft (a unified release of FTOOLS and XANADU software packages) and NuSTAR Data Analysis Software (NuSTARDAS). This Letter made use of the SolarSoft IDL distribution (SSW) from the IDL Astronomy Library. K.C. is supported by a Royal Society Research Fellows Enhancement Award and I.G.H is supported by a Royal Society University Fellowship.
Group:Space Radiation Laboratory, NuSTAR
Funding AgencyGrant Number
Subject Keywords:Solar activity ; Solar corona ; Solar flares ; Solar x-ray flares
Issue or Number:2
Classification Code:Unified Astronomy Thesaurus concepts: Solar activity (1475); Solar corona (1483); Solar flares (1496); Solar x-ray flares (1816)
PubMed Central ID:PMC8780508
Record Number:CaltechAUTHORS:20200422-095631058
Persistent URL:
Official Citation:Kristopher Cooper et al 2020 ApJL 893 L40
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:102715
Deposited By: Tony Diaz
Deposited On:22 Apr 2020 17:15
Last Modified:25 Jan 2022 17:53

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