Abstract

Poster - Splinter MeVSky   (MW-0337)

Constraints on Cosmic-Rays and the MeV Emission from Jupiter’s Atmosphere

Dimitris Tsatsis
University of Würzburg

The Cosmic γ-ray Background (CGB) in the MeV regime remains among the least understood components of diffuse cosmic radia- tion, primarily due to instrumental limitations in detecting faint isotropic emission at MeV energies. We present an indirect method for probing the isotropic emission from soft X-rays to γ-rays through scattered emission in Jupiter’s atmosphere. Using archival observations from SPI (spectrometer aboard INTEGRAL), spanning 22 years of serendipitous Jupiter observations, we analyse the planet as a moving γ-ray point source in the 30 keV–8 MeV range. Our analysis focuses on Jupiter’s γ-ray albedo, created as a result of high-energy photon and cosmic-ray interactions. We performed detailed Monte Carlo simulations to model the yield of Jupiter’s atmosphere to incident radiation, including photons, protons, electrons, positrons and alpha particles. We simulate a 1000 km deep spherical atmosphere with 1 km shell resolution, based on Galileo probe measurements. By comparing emprical and astrophysical models to the SPI data, we find no statistically significant emission from Jupiter. We derive 2σ upper limits across the 30 keV–8 MeV band, which we compare to cutoff power-law, reflected CGB, cosmic-ray-induced, and long-lived mediator dark matter models. We constrain the bremsstrahlung luminosity from Jupiter in the MeV range to 1018 erg/s, which is close to inferred in-situ measurements obtained by Juno/JEDI. While the expected emission from the CGB and cosmic-rays is a factor of 104 and 100 below our upper limits respectively, this work establishes planetary atmospheres as promising indirect probes of diffuse γ-ray backgrounds for future MeV missions.