Flare-accelerated Electrons in the Kappa Distribution from X-Ray Spectra with the Warm-Target Model

Abstract

X-ray observations provide important and valuable insights into the acceleration and propagation of nonthermal electrons during solar flares. Improved X-ray spectral analysis requires a deeper understanding of the dynamics of energetic electrons. Previous studies have demonstrated that the dynamics of accelerated electrons with a few thermal speeds are more complex than those with significantly higher speeds. To better describe the energetic electrons after injection, a model considering energy diffusion and thermalization effects in flare conditions (the warm-target model) has recently been developed for spectral analysis of hard X-rays. This model has demonstrated how the low-energy cutoff, which can hardly be constrained in cold-target modeling, can be determined. However, the power-law form may not be the most suitable representation of injected electrons. The kappa distribution, which is proposed as a physical consequence of electron acceleration, has been applied successfully in RHESSI spectral analysis. In this study, we employ the kappa-form injected electrons in the warm-target model to analyze two M-class flares, observed by RHESSI and STIX, respectively. The best-fit results show that the kappa-form energetic electron spectrum generates lower nonthermal energy than the power-law form when producing a similar photon spectrum in the fit range. We also demonstrated that the fit parameters associated with the kappa-form electron spectrum can be well determined with small uncertainty. Further, the kappa distribution, which covers the entire electron energy range, enables the determination of key electron properties such as total electron number density and average energy at the flare site, providing valuable information on electron acceleration processes.

25 pages, 13 figures, published in the Astrophysical Journal

References in corpus (15)

• The Solar Orbiter mission -- Science overview
• Thermal Diagnostics with the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory: A Validated Method for Differential Emission Measure Inversions
• Global Energetics of Solar Flares: V. Energy Closure in Flares and Coronal Mass Ejections
• Electron Acceleration during Macroscale Magnetic Reconnection
• Relations between concurrent hard X-ray sources in solar flares
• The Formation of Kappa-Distribution Accelerated Electron Populations in Solar Flares
• Chromospheric magnetic field and density structure measurements using hard X-rays in a flaring coronal loop
• Kappa distribution and hard X-ray emission of solar flares
• Hard X-Ray Emission from Partially Occulted Solar Flares: RHESSI Observations in Two Solar Cycles
• On the variation of solar flare coronal x-ray source sizes with energy
• Investigating the differential emission measure and energetics of microflares with combined SDO/AIA and RHESSI observations
• Understanding breaks in solar flares x-ray spectra: Evaluation of a co-spatial return-current model
• Determination of the total accelerated electron rate and power using solar flare hard X-ray spectra
• Multi-point study of the energy release and transport in the 28 March 2022, M4-flare using STIX, EUI, and AIA during the first Solar Orbiter nominal mission perihelion
• The efficiency of electron acceleration during the impulsive phase of a solar flare

Cited by in corpus (1)

• Energy-Containing Electrons in Solar Flares: Improving Hard X-Ray and EUV Diagnostics