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

Gerald H. Share, Ronald J. Murphy

TL;DR

The paper investigates the origin of late-phase gamma-ray emission in SOL2012-06-03 and argues that the second >100 MeV gamma-ray peak marks the onset of Late Phase Gamma-Ray Emission (LPGRE) rather than a new two-phase event. By situating SOL2012-06-03 within the LPGRE framework established from historical events, the authors analyze timing, spectral indices, and flare–CME dynamics to show the second peak is consistent with π-decay emission from protons accelerated by a CME-driven shock. The spectral fits indicate a harder & higher-energy component (e.g., a power-law index of $4.4 \,pm\, 0.5$ above $300$ MeV) and a short delay (~17 s) from the impulsive peak, which can be explained by flare-produced suprathermal protons overtaking the CME-driven shock and returning to the Sun. Collectively, the findings support a CME-shock acceleration origin for LPGRE and imply a high ion-to-electron ratio characteristic of gradual SEP events, distinguishing LPGRE from impulsive flare-associated emission.

Abstract

A recent paper on SOL2012-06-03 reported the detection for the first time of two distinct phases of $>$100 MeV $γ$-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 $π$-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.

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

TL;DR

The paper investigates the origin of late-phase gamma-ray emission in SOL2012-06-03 and argues that the second >100 MeV gamma-ray peak marks the onset of Late Phase Gamma-Ray Emission (LPGRE) rather than a new two-phase event. By situating SOL2012-06-03 within the LPGRE framework established from historical events, the authors analyze timing, spectral indices, and flare–CME dynamics to show the second peak is consistent with π-decay emission from protons accelerated by a CME-driven shock. The spectral fits indicate a harder & higher-energy component (e.g., a power-law index of above MeV) and a short delay (~17 s) from the impulsive peak, which can be explained by flare-produced suprathermal protons overtaking the CME-driven shock and returning to the Sun. Collectively, the findings support a CME-shock acceleration origin for LPGRE and imply a high ion-to-electron ratio characteristic of gradual SEP events, distinguishing LPGRE from impulsive flare-associated emission.

Abstract

A recent paper on SOL2012-06-03 reported the detection for the first time of two distinct phases of 100 MeV -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 -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.
Paper Structure (4 sections, 1 figure)

This paper contains 4 sections, 1 figure.

Table of Contents

  1. Introduction
  2. Characteristics of Late Phase Gamma-Ray Emission
  3. SOL2012-06-03 Second Peak is the Onset of LPGRE
  4. Summary

Figures (1)

  • Figure 1: Three solar eruptions revealing two distinct phases of high-energy emission with the second dominated by protons producing $\pi$-decay emission (GRS 10--50 MeV/$>$65 MeV flux ratios $\gtrapprox$7). The 100--300 keV rates define the impulsive phase.