R. Mewaldt, Psp EPI-Hi Instrument Team
Jul 2, 2021
Proceedings of 36th International Cosmic Ray Conference — PoS(ICRC2019)
The High-Energy Telescope (HET) for the EPI-Hi instrument on Parker Solar Probe (PSP) is designed to measure solar energetic-particle (SEP), interplanetary, and galactic cosmic-ray (CGR) ions with 1≤Z≤30 from ~10 MeV/nuc to several hundred MeV/nuc, and electrons from ~0.5 to ~8 MeV. HET also includes a ‘neutral-particle’ coincidence mode designed to assess the fraction of electron-like events due to g -rays that Compton scatter or pair- produce in the telescope. Based on g -ray observations by SMM, RHESSI and Fermi, along with laboratory calibrations with radioactive g -ray sources, we believe HET is capable of detecting solar g -ray flares, especially when PSP is close to the Sun. This paper illustrates how HET detects solar g -rays and presents “quiet-time background” g -ray spectra (due mainly to g -rays produced by cosmic-ray interactions in surrounding spacecraft material). The estimated g -ray yield from the October 28, 2003 events is used as an example of the HET sensitivity.