On the origin of hard X-ray emissions from the behind-the-limb flare on 2014 September 1

TL;DR

This paper investigates the origin of hard X-ray emissions from a behind-the-limb solar flare, proposing a new Monte Carlo model of particle acceleration at shocks and comparing results with observations.

Contribution

The paper introduces a novel Monte Carlo simulation for particle acceleration at coronal shocks, applied to a specific solar flare event, linking shock acceleration to observed X-ray spectra.

Findings

Model reproduces observed electron spectra after flare peak

Particle diffusion is key to matching measurements

Supports shock acceleration as a source of hard X-rays

Abstract

The origin of hard X-rays and gamma-rays emitted from the solar atmosphere during occulted solar flares is still debated. The hard X-ray emissions could come from flaring loop tops rising above the limb or Coronal Mass Ejections (CME) shock waves, two by-products of energetic solar storms. For the shock scenario to work, accelerated particles must be released on magnetic field lines rooted on the visible disk and precipitate. We present a new Monte Carlo code that computes particle acceleration at shocks propagating along large coronal magnetic loops. A first implementation of the model is carried out for the 2014 September 1 event and the modeled electron spectra are compared with those inferred from Fermi Gamma-ray Burst Monitor (GBM) measurements. When particle diffusion processes are invoked our model can reproduce the hard electron spectra measured by GBM nearly ten minutes after the estimated on-disk hard X-rays appear to have ceased from the flare site.