Evidence that SOL2012-06-03 Late Phase $\gamma$ Rays are Produced by $>$300 MeV Protons from CME-Shock Acceleration of Suprathermals from the Flare

TL;DR

This paper provides evidence that late phase gamma-ray emissions in SOL2012-06-03 are produced by >300 MeV protons accelerated by CME-driven shocks, highlighting a shock acceleration process distinct from impulsive flare emissions.

Contribution

It demonstrates that the late phase gamma-ray peak is associated with shock acceleration of suprathermal protons, offering new insights into the origin of late phase gamma-ray emissions in solar eruptions.

Findings

Late phase gamma-ray emission lasts over 8 minutes.

Delay from impulsive X-ray peak matches shock acceleration timing.

High ion-to-electron ratio consistent with shock-accelerated particles.

Abstract

A recent paper on SOL2012-06-03 reported the detection for the first time of two distinct phases of $>$100 MeV $\gamma$-radiation indicating separate acceleration processes. But such two-phase emission has been seen before and was first observed in SOL1982-06-03. The second phase is known as Late Phase Gamma-Ray Emission (LPGRE) and was cataloged for $>$40 solar eruptions, including SOL2012-06-03. Here we provide evidence that the second SOL2012-06-03 $\pi$-decay peak is the onset of LPGRE that lasted for $>$8 min. Its delay from the impulsive X-ray peak is consistent with the time it would take flare-produced suprathermal protons to overtake the expanding CME and be accelerated by its shock. The high accelerated ion-to-electron ratio in SOL2012-06-03 and other LPGRE events is consistent with the ratio observed in gradual SEP events produced by shocks and is inconsistent with ratios typically found in impulsive flares and solar energetic particle events produced by reconnection.