On the size of the flare associated with the solar proton event in 774 AD
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Abstract
The 774 AD solar proton event (SPE) detected in cosmogenic nuclides had an inferred >1 GV (>430 MeV) fluence estimated to have been ~30–70 times larger than that of the 1956 February 23 ground level event (GLE). The 1956 GLE was itself ~2.5 times larger at >430 MeV than the episode of strong GLE activity from 1989 August–October. We use an inferred soft X-ray (SXR) class of X20 ± 10 for the 1956 February 23 eruptive flare as a bridge to the source flare for the 774 SPE. A correlation of the >200 MeV proton fluences of hard-spectra post-1975 GLEs with the SXR peak fluxes of their associated flares yields an SXR flare class of X285 ± 140 (bolometric energy of ~(1.9 ± 0.7) × 1033 erg) for the 774 flare. This estimate is within theoretical determinations of the largest flare the Sun could produce based on the largest spot group yet observed. Assuming a single eruptive flare source for the 774 SPE, the above estimate indicates that the Sun can produce a threshold-level 1033 erg superflare. If the 774 event originated in two closely timed, equal-fluence SPEs, the inferred flare size drops to X180 ± 90 (~(1.4 ± 0.5) × 1033 erg). We speculate on favorable solar conditions that can lead to enhanced shock acceleration of high-energy protons in eruptive flares.
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | On the size of the flare associated with the solar proton event in 774 AD |
| Series title | Astrophysical Journal |
| DOI | 10.3847/1538-4357/abad93 |
| Volume | 903 |
| Issue | 1 |
| Year Published | 2020 |
| Language | English |
| Publisher | American Astronomical Society |
| Contributing office(s) | Geologic Hazards Science Center |
| Google Analytic Metrics | Metrics page |