NuSTAR Observation of a Minuscule Microflare in a Solar Active Region

Creators: Cooper, Kristopher; Hannah, Iain G.; Grefenstette, Brian W.; Glesener, Lindsay; Krucker, Säm; Hudson, Hugh S.; White, Stephen M.; Smith, David M.

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 1.1 × 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.

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.

Attached Files

Published - Cooper_2020_ApJL_893_L40.pdf

Accepted Version - 2004.11176.pdf

Files

Cooper_2020_ApJL_893_L40.pdf

Files (2.0 MB)

Name	Size	Download all
Cooper_2020_ApJL_893_L40.pdf md5:f443054968d8905c35a7b03438103712	1.1 MB	Preview Download
2004.11176.pdf md5:28f5bcdbcd972bf16c8a2fea77b1405b	920.0 kB	Preview Download

Additional details

	All versions	This version
Views	0	0
Downloads	0	0
Data volume	0 Bytes	0 Bytes