Erlangen 2026 – wissenschaftliches Programm

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EP: Fachverband Extraterrestrische Physik

EP 11: Planets and Small Bodies

EP 11.4: Vortrag

Freitag, 20. März 2026, 12:00–12:15, KH 01.019

Time-Variability of the Galactic Positron Annihilation Signal — •Rudi Reinhardt and Thomas Siegert — Julius-Maximilians-Universität Würzburg, Würzburg, Germany

The interactions of low-energy cosmic-rays with asteroids might lead to a measurable variable gamma-ray foreground emission within our Solar system. Siegert (2024) modeled the spatial distribution of all relevant asteroid populations (Main Belt Asteroids, Jovian and Neptunian Trojans and the Kuiper Belt) to calculate their appearances by line-of-sight integrations. The signal is expected to vary in time due to the relative motion of Earth and the asteroids. In this work we used 20 yr of INTEGRAL/SPI data to search for this time-variable foreground albedo in both, the 511 keV line and the ortho-Positronium (oPs) continuum. Since the Galaxy is bright in the bulge at 511 keV, we can determine its variability on a two year timescale, which allows us to constrain the possible contributions from all asteroid families. Our analysis shows no significant emission signal for all considered populations. However, we find a significant 511 keV signal in the vicinity of the Galactic center, which may mimic variable diffuse emission unless its time variability is taken into account. In a 20x20 deg2 region around the Galactic center, we find several point-like hotspots which coincide spatially with the distribution of globular clusters. Preliminary results of GEANT4 simulations of electromagnetic and hadronic interactions of cosmic-rays with asteroids agree with contemporaneous simulations by DeGaetano et al. (2023) using FLUKA, with fluxes being several orders of magnitude smaller than previously estimated.

Keywords: Cosmic-rays; Gamma-rays; Asteroids; Positrons; Time-variability