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NuSTAR observations of a repeatedly microflaring active region
Kristopher Cooper1, Iain G Hannah1, Brian W Grefenstette2
1School of Physics & Astronomy, University of Glasgow, University Avenue, Glasgow G12 8QQ, UK.
Monthly Notices of the Royal Astronomical Society
|January 17, 2022
Summary
Researchers studied 10 microflares from active region 12721, finding energies up to 10 MK. One microflare showed direct evidence of accelerated electrons, indicating the need for sensitive observations.
Area of Science:
- Solar physics
- Plasma astrophysics
Background:
- Microflares are small-scale solar eruptions.
- Understanding microflare energy release is crucial for solar physics.
Purpose of the Study:
- To investigate the properties of microflares using multi-instrument observations.
- To determine the energy, temperature, and electron acceleration in microflares.
Main Methods:
- Utilized data from the Nuclear Spectroscopic Telescope Array (NuSTAR) and the Solar Dynamics Observatory (SDO).
- Analyzed X-ray, extreme-ultraviolet (EUV), and photospheric magnetic field data.
- Characterized spatial, temporal, and spectral properties of 10 microflares from active region 12721.
Main Results:
- Microflare energies ranged from 10^26 to 10^28 erg, reaching temperatures up to 10 MK.
- One microflare (A0.1 class) exhibited non-thermal hard X-ray emission, indicating accelerated electrons.
- X-ray profiles matched EUV sources in 4 cases, suggesting hotter plasma (>5 MK) than the active region core.
- Photospheric magnetic flux cancellation/emergence was observed at the footpoints of eight microflares.
Conclusions:
- Microflares can accelerate electrons, as evidenced by hard X-ray emission in faint events.
- Observations sensitive to hotter plasma are necessary to fully understand microflare dynamics.
- Magnetic flux changes in the photosphere are linked to microflare occurrences.
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