NuSTAR Observation of a Minuscule Microflare in a Solar Active Region

被引：21
作者：
Cooper, Kristopher [1 ]
Hannah, Iain G. [1 ]
Grefenstette, Brian W. [2 ]
Glesener, Lindsay [3 ]
Krucker, Saem [4 ,5 ]
Hudson, Hugh S. [1 ,5 ]
White, Stephen M. [6 ]
Smith, David M. [7 ,8 ]
机构：
[1] Univ Glasgow, Sch Phys Astron, Glasgow G12 8QQ, Lanark, Scotland
[2] CALTECH, Cahill Ctr Astrophys, 1216 East Calif Blvd, Pasadena, CA 91125 USA
[3] Univ Minnesota Twin Cities, Sch Phys & Astron, Minneapolis, MN 55455 USA
[4] Univ Appl Sci & Arts Northwestern Switzerland, CH-5210 Windisch, Switzerland
[5] Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA
[6] US Air Force, Res Lab, Space Vehicles Directorate, Kirtland AFB, NM 87123 USA
[7] Univ Calif Santa Cruz, Santa Cruz Inst Particle Phys, Santa Cruz, CA 95064 USA
[8] Univ Calif Santa Cruz, Dept Phys, Santa Cruz, CA 95064 USA
来源：
ASTROPHYSICAL JOURNAL LETTERS | 2020年 / 893卷 / 02期
基金：
美国国家航空航天局;
关键词：
Solar activity; Solar corona; Solar flares; Solar x-ray flares; STATISTICS; NANOFLARES; CORONA; PLASMA;
D O I：
10.3847/2041-8213/ab873e
中图分类号：
P1 [天文学];
学科分类号：
0704 ;
摘要：
We present X-ray imaging spectroscopy of one of the weakest active region (AR) microflares ever studied. The microflare occurred at similar to 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 A 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 x 10(26) erg. It reaches temperatures of 6.7 MK with an emission measure of 8.0 x 10(43) 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.
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页数：7
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