Fermi-LAT observations of the 2017 September 10$^{th}$ solar flare

TL;DR

This paper reports the first detailed observations of a long-duration high-energy gamma-ray solar flare associated with a Ground Level Enhancement, revealing insights into proton acceleration phases and flare localization.

Contribution

It provides the first localization and analysis of a long-duration gamma-ray flare linked to a GLE, highlighting two proton acceleration phases and their possible mechanisms.

Findings

Gamma-ray emission lasted over 12 hours, covering impulsive and extended phases.

Localization consistent with the active region for over 6 hours.

Evidence of two proton acceleration phases, with the second linked to CME-driven shock.

Abstract

The Fermi-Large Area Telescope (LAT) detection of the X8.2 GOES class solar flare of 2017 September 10 provides for the first time observations of a long duration high-energy gamma-ray flare associated with a Ground Level Enhancement (GLE). The >100 MeV emission from this flare lasted for more than 12 hours covering both the impulsive and extended phase. We present the localization of the gamma-ray emission and find that it is consistent with the active region (AR) from which the flare occurred over a period lasting more than 6 hours contrary to what was found for the 2012 March 7 flares. The temporal variation of the proton index inferred from the gamma-ray data seems to suggest two phases in acceleration of the proton population. Based on timing arguments we interpret the second phase to be tied to the acceleration mechanism powering the GLE, believed to be particle acceleration at a coronal shock driven by the CME.