Constraints on the Electron Acceleration Process in Solar Flare: A Case Study

Abstract

Solar flares are a major particle accelerator in the solar system (Reames, 2015). In the standard flare model (aka CSHKP model) (Carmichael, 1964;Hirayama, 1974;Kopp & Pneuman, 1976;Sturrock, 1966), magnetic reconnection at the reconnection current sheet powers the particle acceleration process. Recent RHESSI imaging observations (Liu et al., 2013) have revealed that energetic electrons may be accelerated at reconnection exhausts. It is possible that energetic electrons propagating downward and upward undergo different acceleration processes. In the standard flare model, the reconnection is between close field lines so electrons accelerated in the upward propagating reconnection exhaust can not reach 1 AU unless interchange reconnection is involved (Masson et al., 2013) (Note that however, a closed loop from a preceding CME can extend beyond 1 AU. If magnetic reconnection occurs between the two legs of this closed loop, then electrons can propagate into 1 AU along a closed loop). Electrons can be accelerated at these interchange reconnection sites as well. In the early work of Heyvaerts et al. (1977), flares are driven by interchange reconnection alone, without closed field reconnection. One important implication of Heyvaerts et al. (1977)

Statistical Study of Release Time and Its Energy Dependence of In Situ Energetic Electrons in Impulsive Solar Flares

“…In this article, we perform a statistical study of the release time for 29 impulsive SEE events from 2002 to 2016 using in situ electron data from WIND/3DP and HXR observation from RHESSI and Fermi/GBM. Based on the recently developed FVDA (Zhao et al, 2019), we examined the release time of both the outward-and downward-propagating near-relativistic electrons and showed that for all events, there is a distinct time delay, mainly distributed between 0 and 1,000 s, which is consistent with the case study of G. and G. Li et al (2021). The release time of in situ electrons also shows clear energy dependence with higher energy electrons released later, consistent with a time-dependent acceleration process.…”

“…In a recent paper, W. Wang et al (2021) examined the spectral relationship between HXR-producing electrons and SEEs and also concluded that the HXR-producing electrons and SEE electrons are of two different populations. They also suggested that two (or more) reconnection processes may occur at the reconnection site, and the HXR-generating electrons are electrons that experience two consecutive accelerations, that is, they are downward-traveling electrons produced at the first reconnection site which occur high in the corona.…”

“…In the 2016‐07‐23 event, G. Li et al. (2021) examined the energy dependence of the release times and found that the delay can be fitted by a power law form. From the power law index of the fitting, they inferred the Magnetohydrodynamics turbulence power spectrum at the acceleration site.…”

“…(2020) and G. Li et al. (2021) tested this idea of simultaneous release in two impulsive energetic electron events, the 2001‐04‐25 event and the 2016‐07‐23 event. In both events, in situ electrons were observed by the 3D Plasma and Energetic Particle (3DP) instruments on WIND.…”

“…In 15 events, in situ electron observation for more than five energy channels are obtained. For these events, we further apply the analysis in G. Li et al (2021) to fit the energy release time delay by a power law of the electron momentum. For 9 out of 15 events, reasonable fittings were obtained and the fitting results are shown in Table 2 and Figure 5.…”