Observations of the Quiet Sun During the Deepest Solar Minimum of the Past Century with Chandrayaan-2 XSM -- Sub-A Class Microflares Outside Active Regions

Abstract

Solar flares, with energies ranging over several orders of magnitude, result from impulsive release of energy due to magnetic reconnection in the corona. Barring a handful, almost all microflares observed in X-rays are associated with the solar active regions. Here we present, for the first time, a comprehensive analysis of a large sample of quiet Sun microflares observed in soft X-rays by the Solar X-ray Monitor (XSM) on board the Chandrayaan-2 mission during the 2019-20 solar minimum. A total of 98 microflares having peak flux below GOES A-level were observed by the XSM during observations spanning 76 days. By using the derived plasma temperature and emission measure of these events obtained by fitting the XSM spectra along with volume estimates from concurrent imaging observations in EUV with the Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA), we estimated their thermal energies to be ranging from 3e26 to 6e27 erg. We present the frequency distribution of the quiet Sun microflares with energy and discuss the implications of these observations of small-scale magnetic reconnection events outside active regions on coronal heating.

Accepted for publication in ApJL; 13 pages, 5 figures; All figures of figure set 3 available in the tar file

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Cited by in corpus (17)

• NuSTAR observations of a repeatedly microflaring active region
• Coronal Elemental Abundances during A-class Solar Flares Observed by Chandrayaan-2 XSM
• Observations of the Quiet Sun During the Deepest Solar Minimum of the Past Century with Chandrayaan-2 XSM -- Elemental Abundances in the Quiescent Corona
• Soft X-ray Spectral Diagnostics of Multi-thermal Plasma in Solar Flares with Chandrayaan-2 XSM
• Role of small-scale impulsive events in heating the X-ray bright points of the quiet Sun
• Detection of weak ubiquitous impulsive nonthermal emissions from the solar corona
• Multi-wavelength observations by XSM, Hinode and SDO of an active region. Chemical abundances and temperatures
• Coronal energy release by MHD avalanches. Effects on a structured, active region, multi-threaded coronal loop
• Turbulence dynamics and flow speeds in the inner solar corona: Results from radio-sounding experiments by the Akatsuki spacecraft
• Nanoflare Heating of the Solar Corona Observed in X-rays
• Multifrequency microwave imaging of weak transients from the quiet solar corona
• Solar flare catalog from 3 years of Chandrayaan-2 XSM observations
• Detecting non-thermal emission in a solar microflare using nested sampling
• Radio, X-ray and extreme-ultraviolet observations of weak energy releases in the `quiet' Sun
• Quiet Sun impulsive events observed with NuSTAR during solar minimum
• Evolution of Elemental Abundances During B-Class Solar Flares: Soft X-ray Spectral Measurements with Chandrayaan-2 XSM
• Limits on the axion-photon coupling from Chandrayaan-2 observations