Authors: J. Grant Mitchell (NASA/GSFC), G. A. de Nolfo (NASA/GSFC), E. R. Christian (NASA/GSFC), R. A. Leske (Caltech), J. M. Ryan (UNH), J. T. Vievering (JHUAPL), M. E. Hill (JHUAPL), A. W. Labrador (Caltech), M. E. Wiedenbeck (JPL), D. J. McComas (Princeton), C. M. S. Cohen (Caltech), R. L. McNutt Jr. (JHUAPL), R. A. Mewaldt (Caltech), D. G. Mitchell (JHUAPL), J. S. Rankin (Princeton), N. A. Schwadron (UNH)

High-energy neutral solar radiation in the form of gamma-rays and neutrons is produced as secondary products in solar flares.  The characteristics of this emission can provide key information regarding the energization of charged particles, particularly when primary particles remain trapped in the corona.  The Integrated Science Investigation of the Sun (ISOIS) suite on Parker Solar Probe is composed of instruments primarily intended to measure energetic charged particles.  However, the High Energy Telescope (HET) in ISOIS was also designed with a supplementary “neutral mode” intended to measure gamma-rays and neutrons.  HET observed its first clear solar gamma-ray event in connection with a hard X-ray flare, the eruption of a coronal mass ejection, and a solar energetic particle event on 2022 September 5.  A coincident enhancement in the lower-energy Energetic Particle Instrument (EPI-Lo) was also observed, likely produced by incident solar gamma-rays despite the EPI-Lo instrument not having any special neutral measurement capabilities.  We use Monte Carlo modeling to reconstruct the incident gamma-ray spectrum based on the measured spectrum to demonstrate that the combination of ISOIS instruments can measure hard X-rays and gamma-rays from ~60 keV – 7 MeV.  We present the capabilities of the ISOIS instruments to measure solar gamma-rays and analyze the characteristics of this event.  The capability of the ISOIS instruments to measure gamma-rays is important for the study of this population due to the very limited instruments currently observing the Sun in gamma-rays.