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Soft X-ray Spectral Analysis of Solar flare Onsets using the Dual-zone X-ray Solar Spectrometer (DAXSS) Measurements

Presentation #301.07 in the session Activity Prediction from Active Regions to Flare Onset.

Published onSep 18, 2023
Soft X-ray Spectral Analysis of Solar flare Onsets using the Dual-zone X-ray Solar Spectrometer (DAXSS) Measurements

Analysis of soft X-ray emissions during the course of solar flares can provide insight into the localized flaring-plasma conditions, which helps in understanding the physical processes leading to impulsive energy release during solar flares. New soft X-ray measurements from the third-generation NASA-funded Miniature X-Ray Solar Spectrometer (MinXSS), also known as the Dual-zone Aperture X-ray Solar Spectrometer (DAXSS), are introduced with emphasis on their application for the study of solar flares. Detailed analysis of solar flare events that occurred in 2022 and 2023 are presented including a C6.7 flare on 2022-03-15, an M5.7 flare on 2022-05-04, and a C2.6 flare on 2022-03-06. These flares are chosen such that they have a distinct “onset phase” before the main impulsive phase, characterized by elevated soft X-ray emissions even before the impulsive phase. The temporal evolution of localized plasma temperature, emission measure, and elemental abundance factors during the flare are analyzed by fitting the DAXSS spectra to the Astrophysical Plasma Emission Code (APEC) model spectra using PyXSPEC. Due to the improved energy resolution of the DAXSS instrument, the soft X-ray plasma emission spectra can be fit to multi-temperature models (for example a 4-Temperature model) with varying elemental abundance values (such as low first-ionization potential (FIP) elements including Si, Ca, Fe, Mg, and S) to obtain higher-fidelity fit results. The abundance factors follow a trend of falling below the pre-flare values during the impulsive phase of the flare and slowly recovering back to the original value during the gradual phase. Analysis of the plasma temperatures indicates the plasma is already at a very high temperature (10-15 MK) during the onset period of the flare. In addition, the abundance decreases for some elements at the beginning of the onset phase and then has some recovery before the impulsive phase begins. These flares are also analyzed using running-difference images of the 193A channel of the Atmospheric Imaging Assembly (AIA), indicating upward movement of plasma loops during the onset phase. As the onset phase has similar properties as the impulsive phase, the onset phase might be a pre-conditioning effect for some flares.

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