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

Abstract

The X9.3 flare SOL20170906T11:55 was observed by the CsI detector aboard the first Chinese Xray observatory Hard X-ray Modulation telescope (Insight-HXMT). By using wavelets method, we report about 22s 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 ∼ 1.8 before the peak, ∼ 2.0 around the flare peak, to ∼ 1.8 again. The gyrosynchrotron microwave spectral analysis reveals a 36.6 ± 0.6 radius gyrosynchrotron source with mean transverse magnetic field around 608.2 Gauss, and the penetrated ≥ 10 keV non-thermal electron density is about 10 6.7 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 higherfrequency light curves. The temporally spectral analysis reveals that those non-thermal electrons are accelerated by repeated magnetic reconnection, likely from a lower corona source.

Detection of flare multi-periodic pulsations in mid-ultraviolet Balmer continuum, Ly-alpha, hard X-ray, and radio emissions simultaneously

“…In this study, we report the multi-periodic QPPs during the flare impulsive phase in Lyα, MUV Balmer continuum, low-frequency radio and HXR channels simultaneously. The short periods of 20−40 s are detected during ∼11:56−11:59 UT, which are similar to previous findings in the radio, HXR and γ-ray channels (Li et al 2020a;Zhang et al 2021). However, they could not study the QPP behaviors after 11:59 UT, largely due to their observational limitations.…”

“…They found that the QPP periods varied from around 12 s to 25 s in the thermal emission during the flare impulsive and decay phases, and attributed them to be the sausage oscillations of flaring loops. Next, Li et al (2020a) studied the flare-related QPPs with periods of about 20−30 s at channels of radio, HXR and γ-ray during the impulsive phase, and the similar periods were also reported by Zhang et al (2021). Then, Karlický & Rybák (2020) detected multiple periods (i.e., 1−2 s, 5.3−8.5 s and 11−30 s) mainly in the radio emission during the pre-impulsive and impulsive phases of the X9.3 flare.…”

“…Here, the long periods of ∼50−55 s are also found from roughly 11:57 UT to 12:02 UT. We would like to point out that a much longer period of roughly 80 s could also be seen in the LYRA data, and it is mostly caused by the two main pulses during ∼11:55:40−11:58:20 UT in the raw light curves, which are similar to the intermittent feature in the HXR emission (Zhang et al 2021). However, it is not suitable for a typical QPP, since it only remains two cycles (e.g., two pulses).…”

“…However, it is impossible to determine the duration of the short periods, especially the lifetime of periods between 50−55 s, since they are also seen at the border edges of the strongest power in the wavelet power spectra in Figure A. We also notice that the 80-s period has been studied in the flare emission at wavelengths of Lyα (Li et al 2020d) and HXR emission (Zhang et al 2021), respectively. Therefore, we only focused on the short periods of ∼20−55 s in this study.…”

“…The QPP behaviors of the X9.3 flare has been studied at wavelengths of radio, SXR, HXR, and even γ-ray (Kolotkov et al 2018;Karlický & Rybák 2020;Li et al 2020a;Zhang et al 2021). Kolotkov et al (2018) first investigated the QPP signals during the X9.3 flare.…”