Origin of seed particles injected into coronal loops during LDGRFs

Determine whether the seed particle population injected into the large-scale coronal loops implicated in long-duration gamma-ray flares originates from flare-associated processes in the low corona or from particles accelerated at CME-driven shocks, in order to clarify the source of the ions that are subsequently trapped and accelerated within the loops.

Background

The paper contrasts two leading scenarios for producing the >100 MeV gamma rays in long-duration gamma-ray flares (LDGRFs): acceleration at CME-driven shocks with back-precipitation to the solar surface, and local trapping plus stochastic acceleration within large-scale coronal loops. The authors highlight observational and theoretical challenges to the CME-driven shock paradigm, including magnetic mirroring and weak late-time shock acceleration at large heliocentric distances.

Within the loop scenario, energetic ions must be injected into giant, quasi-static magnetic loops and then accelerated (e.g., by second-order Fermi processes) to GeV energies before precipitating at the footpoints to produce gamma rays. A key unresolved issue is whether the initial seed population entering these loops is supplied by flare-associated processes (which naturally occur in closed-field regions) or by CME-driven shocks (whose geometry and field-line connectivity make injection into closed loops less likely).