Authors: R.A. Leske(1), J.G. Mitchell(2), C.M.S. Cohen(1), A.C. Cummings(1), A.W. Labrador(1), G.D. Muro (1), M.E. Wiedenbeck(3), Z. Xu (1), E.R. Christian(2), G.A. de Nolfo(2), D.J. McComas(4), N.A. Schwadron(4,5) 1) California Institute of Technology, Pasadena, CA 91125, USA 2) Goddard Space Flight Center, Greenbelt, MD 20771, USA 3) Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA 4) Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA 5) University of New Hampshire, Durham, NH 03824, USA

The ISOIS suite on Parker Solar Probe is primarily intended to measure charged energetic particles. However, the ISOIS EPI-Hi/HET telescope also detects interactions by neutrals that result in a charged particle (e.g., a gamma ray Compton scattering and producing an electron or a neutron undergoing a nuclear interaction with the silicon and creating a proton) if that particle stops in a shielded central region of silicon detectors without triggering the surrounding guards or outer detectors. Locally produced neutrals are created by solar energetic particles (SEPs) and galactic cosmic rays that interact with material in the spacecraft or instrument, but emission by solar flares may be distinguished from this background if the neutral rate increases well before the arrival of SEP particles. To date we have found at least 9 gamma-ray flares in the HET neutral data, ranging in duration from <1 minute to ~15 minutes with intensities up to ~100 times that of the quiet-time background level. Although statistics are still meager, there may be a suggestion that these events are often intrinsically small and are only detected due to Parker’s proximity to the Sun: 5 of the 9 events (56%) were observed when Parker was <0.1 au from the Sun, despite the fact that <3% of the HET observation time was at these close distances. Prior to commanding in June 2023, instrumental issues prevented HET from detecting neutrons; we are in the process of assessing whether any of the “gamma-ray” signals seen in the 5 events since then might in fact be due to neutrons instead.

We present time profiles and energy spectra of the HET solar neutral observations, describe the associated SEP events, and compare with X-ray and radio observations in these events where available.