NuSTAR observations of a repeatedly microflaring active region
Abstract
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 1026–1028 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 × 1024 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.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Aug 19, 2021
- Source ID
- 10.1093/mnras/stab2283
Entities
People
- Brian Grefenstette
- David M Smith
- Hugh S. Hudson
- Iain G. Hannah
- Jessie Duncan
- Kristopher Cooper
- Lindsay Glesener
- Stephen White
- Säm Krucker
Organizations
- Air Force Research Laboratory
- California Institute of Technology
- National Aeronautics and Space Administration
- University of California
- University of Glasgow
- University of Minnesota