| Autor: |
Cooper K; School of Physics & Astronomy, University of Glasgow, University Avenue, Glasgow G12 8QQ, UK., Hannah IG; School of Physics & Astronomy, University of Glasgow, University Avenue, Glasgow G12 8QQ, UK., Grefenstette BW; Cahill Center for Astrophysics, California Institute of Technology, 1216 East California Boulevard, Pasadena, CA 91125, USA., Glesener L; School of Physics & Astronomy, University of Minnesota Twin Cities, Minneapolis, MN 55455, USA., Krucker S; School of Engineering, University of Applied Sciences and Arts Northwestern Switzerland, CH-5210 Windisch, Switzerland.; Space Sciences Laboratory, University of California, Berkeley, CA 94720, USA., Hudson HS; School of Physics & Astronomy, University of Glasgow, University Avenue, Glasgow G12 8QQ, UK.; Space Sciences Laboratory, University of California, Berkeley, CA 94720, USA., White SM; Air Force Research Laboratory, Space Vehicles Directorate, Kirtland AFB, NM 87123, USA., Smith DM; Santa Cruz Institute of Particle Physics and Department of Physics, University of California, Santa Cruz, CA 95064, USA., Duncan J; School of Physics & Astronomy, University of Minnesota Twin Cities, Minneapolis, MN 55455, USA. |
| Abstrakt: |
We investigate the spatial, temporal, and spectral properties of 10 microflares from AR12721 on 2018 September 9 and 10 observed in X-rays using the Nuclear Spectroscopic Telescope ARray and the Solar Dynamic Observatory's Atmospheric Imaging Assembly and Helioseismic and Magnetic Imager. We find GOES sub-A class equivalent microflare energies of 10 26 -10 28 erg reaching temperatures up to 10 MK with consistent quiescent or hot active region (AR) core plasma temperatures of 3-4 MK. One microflare (SOL2018-09-09T10:33), with an equivalent GOES class of A0.1, has non-thermal hard X-ray emission during its impulsive phase (of non-thermal power ~7 × 10 24 erg s -1 ) making it one of the faintest X-ray microflares to have direct evidence for accelerated electrons. In 4 of the 10 microflares, we find that the X-ray time profile matches fainter and more transient sources in the extreme-ultraviolet, highlighting the need for observations sensitive to only the hottest material that reaches temperatures higher than those of the AR core (>5 MK). Evidence for corresponding photospheric magnetic flux cancellation/emergence present at the footpoints of eight microflares is also observed. |
