Solar Neutrons Observed from September 4 to 10, 2017 by SEDA-FIB

TL;DR

This study reports the detection of solar neutrons from multiple flares in September 2017 by the SEDA-FIB detector on the ISS, providing insights into high-energy particle acceleration during solar events.

Contribution

It presents the first observations of solar neutrons from specific flares in 2017 and analyzes their relation to electron acceleration, suggesting shock acceleration as a plausible mechanism.

Findings

Detected solar neutrons from nine large flares in September 2017.

Identified two flares with clear neutron signals linked to high-energy electron acceleration.

Proposed shock acceleration as a possible explanation for particle energization.

Abstract

The SEDA-FIB is a detector designed to measure solar neutrons. This solar neutron detector was operated onboard the ISS on July 16, 2009 and March 31, 2018. Eighteen large solar flares were later observed by the GOES satellite in solar active region 12673 that appeared on September 4 and lasted until September 10, 2017, with intensity higher than > M2. In nine of those solar flares, the SEDA-FIB detected clear signals of solar neutrons, along with five minor excesses. Among these events, we focus on two associated with the flares of X2.2 (SOL2017-09-06) and X8.2 (SOL2017-09-10) that share a common feature: a process of accelerating electrons into high energies as clearly recorded by the FERMI-GBM detector. These events may provide us with useful information to elucidate the ion acceleration process. The X8.2 event was a limb flare that proved adequate for fixing the parameters needed to explain the process of particle acceleration into high energies. According to our analysis, the electron acceleration process may possibly be explained by the shock acceleration model. However, we found that it would be difficult to explain the simultaneous acceleration of ions with electrons, unless the ions were preheated prior to their rapid acceleration.