Comparing Long-duration Gamma-Ray Flares and High-energy Solar Energetic Particles

Abstract

Little is known about the origin of the high-energy and sustained emission from solar Long-Duration Gamma-Ray Flares (LDGRFs), identified with the Compton Gamma Ray Observatory (CGRO), the Solar Maximum Mission (SMM), and now Fermi. Though Fermi/Large Area Space Telescope (LAT) has identified dozens of flares with LDGRF signature, the nature of this phenomenon has been a challenge to explain both due to the extreme energies and long durations. The highest-energy emission has generally been attributed to pion production from the interaction of 300 MeV protons with the ambient matter. The extended duration suggests that particle acceleration occurs over large volumes extending high in the corona, either from stochastic acceleration within large coronal loops or from back precipitation from coronal mass ejection driven shocks. It is possible to test these models by making direct comparison between the properties of the accelerated ion population producing the γ-ray emission derived from the Fermi/LAT observations, and the characteristics of solar energetic particles (SEPs) measured by the Payload for Matter-Antimatter Exploration and Light Nuclei Astrophysics (PAMELA) spacecraft in the energy range corresponding to the pionrelated emission detected with Fermi. For fourteen of these events we compare the two populations -SEPs in space and the interacting particles at the Sun -and discuss the implications in terms of potential sources. Our analysis shows that the two proton numbers are poorly correlated, with Corresponding author: G. A. de Nolfo georgia.a.denolfo@nasa.gov Corresponding author: A. Bruno alessandro.bruno-1@nasa.gov 2 de Nolfo et al.their ratio spanning more than five orders of magnitude, suggesting that the back precipitation of shock-acceleration particles is unlikely the source of the LDGRF emission.

3D propagation of relativistic solar protons through interplanetary space

“…2 are very similar at early times is that it takes a finite amount of time for particles to drift down to the HCS in the A + case, at which point HCS drifts set in. Our findings on the influence of IMF polarity on number of crossings per particle is confirmed by a completely independent test particle simulation code with flat HCS (Chollet et al 2010;de Nolfo et al 2019). We note that changing the parameters of the HCS (for example the tilt angle) does not affect N cross strongly and that its energy dependence (fewer crossings at higher energies) is a result of the particle populations at high energies propagating faster towards the outer heliosphere.…”

“…The new observations call for modelling tools that describe the acceleration and propagation of particles at these energies. In addition, simulations of propagation through the IMF are necessary to relate the detections of high energy SEPs at 1 AU to the numbers of interacting particles at the Sun, which produce solar γ-ray events detected by the Fermi Gammaray Space Telescope (de Nolfo et al 2019;Share et al 2018;Klein et al 2018).…”

Positron Processes in the Sun

“…The average duration of these gamma-ray events is about 9.7 h and with six events lasting for more than 12 h [32,33], including an event that lasted for almost a day. The time-extended events are known by different names "long duration gamma-ray flare (LDGRF)" [34,35], "sustained gamma-ray emission (SGRE)" [33,36], and "late-phase gamma-ray emission (LPGRE)" [32]. The Fermi/LAT observations have revived the interest in the origin of the high-energy particles in these events because the accelerator needs to inject >300 MeV ions toward the chromosphere/photosphere to produce the pions required for the gamma-ray events.…”

Monitoring and research of high-energy solar flare emissions with GECAM

“…http://engine.scichina.com/doi/10.1360/SSPMA-2020-0012 能辐射持续时间从数个小时到20 h不等, 主要由高 于500 MeV质子引起的π介子衰变产生. 观测还发 现, 这些长持续伽马耀斑通常都伴随着快速CME以 及硬X射线辐射 [54] . 长时间伽马耀斑背后的物理机 制目前尚不清楚, GECAM具有较大的探测面积, 这 将为揭示长时间伽马耀斑创造更好的硬X射线观测 数据样本.…”