Non-thermal electron energization during the impulsive phase of an X9.3 flare revealed by Insight-HXMT

TL;DR

This study used Insight-HXMT observations to analyze a powerful X9.3 solar flare, revealing quasiperiodic pulsations, non-thermal electron acceleration, and magnetic reconnection processes during the impulsive phase.

Contribution

It provides new insights into electron energization and magnetic field evolution during a major solar flare using high-energy X-ray and microwave data.

Findings

Detected 22 s quasiperiodic pulsations during the impulsive phase.

Observed evolution of gamma-ray spectra with photon index changes.

Identified a steady gyrosynchrotron source with evolving magnetic field and electron density.

Abstract

The X9.3 flare SOL20170906T11:55 was observed by the CsI detector aboard the first Chinese X-ray observatory Hard X-ray Modulation telescope (Insight-HXMT). By using wavelets method, we report about 22 s quasiperiodic pulsations(QPPs) during the impulsive phase. And the spectra from 100 keV to 800 keV showed the evolution with the gamma-ray flux, of a power-law photon index from $\sim 1.8$ before the peak, $\sim 2.0$ around the flare peak, to $\sim 1.8$ again. The gyrosynchrotron microwave spectral analysis reveals a $36.6 \pm 0.6 \arcsec$ radius gyrosynchrotron source with mean transverse magnetic field around 608.2 Gauss, and the penetrated $\ge$ 10 keV non-thermal electron density is about $10^{6.7} \mathrm{cm}^{-3}$ at peak time. The magnetic field strength followed the evolution of high-frequency radio flux. Further gyrosynchrotron source modeling analysis implies that there exists a quite steady gyrosynchrotron source, the non-thermal electron density and transverse magnetic field evolution are similar to higher-frequency light curves. The temporally spectral analysis reveals that those non-thermal electrons are accelerated by repeated magnetic reconnection, likely from a lower corona source.