Identify mechanisms of long-duration solar gamma-ray emission

Determine the physical mechanism(s) responsible for long-duration gamma-ray emission from the Sun, discriminating among CME-driven shock back-precipitation of ions, extended coronal acceleration, and trapping in magnetic loops, and establish the conditions under which each operates.

Background

Solar flares produce gamma-ray emission, but some events exhibit much longer durations than typical flare-associated emission, implying additional or different acceleration and transport processes.

Resolving the mechanism is critical for interpreting particle acceleration pathways, for relating electromagnetic flare signatures to SEP production, and for evaluating whether analogous diagnostics could be used for other stars.

References

Long-duration gamma-ray events, in which the emission lasts much longer than that typically associated with solar flares, suggest that reconnection-based particle acceleration, expected to be short-lived, is not the sole cause of solar gamma rays (Ryan, 2000; Share et al., 2018). The mechanism to produce this extended emission has not been determined.

— The Exospace Weather Frontier  (2511.02871 - Loyd et al., 4 Nov 2025) in Section 5.6.1