NuSTAR observation of a minuscule microflare in a solar active region

Cooper, K., Hannah, I. , Grenfenstette, B. W., Glesener, L., Krucker, S., Hudson, H. , White, S. and Smith, D. M. (2020) NuSTAR observation of a minuscule microflare in a solar active region. Astrophysical Journal Letters, 893(2), L40. (doi: 10.3847/2041-8213/ab873e)

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Abstract

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 1.1e26 erg. It reaches temperatures of 6.7 MK with an emission measure of 8.0e43 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:Articles (Letter)
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Hudson, Dr Hugh and Hannah, Dr Iain and Cooper, Kristopher
Authors: Cooper, K., Hannah, I., Grenfenstette, B. W., Glesener, L., Krucker, S., Hudson, H., White, S., and Smith, D. M.
Subjects:Q Science > QB Astronomy
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Astrophysical Journal Letters
Publisher:American Astronomical Society
ISSN:2041-8205
ISSN (Online):2041-8213
Copyright Holders:Copyright © 2020 The American Astronomical Society
First Published:First published in Astrophysical Journal Letters 893(2):L40
Publisher Policy:Reproduced in accordance with the publisher copyright policy
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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
168652The many scales of flaring energy release on the SunIain HannahThe Royal Society (ROYSOC)UF120063P&S - Physics & Astronomy
301935URF RenewalIain HannahThe Royal Society (ROYSOC)URF/R/180010P&S - Physics & Astronomy
301903The high energy emission from small solar flaresIain HannahThe Royal Society (ROYSOC)N/AP&S - Physics & Astronomy