Abstract

Poster - Splinter MeVSky   (MW-0337)

Electron-Positron Annihilation in Globular Clusters and the 511 keV – 2.223 MeV Correlation

Manuel Skalka
University of Würzburg

The 2.223 MeV gamma-ray line, originating from neutron capture on hydrogen, is a crucial but elusive diagnostic of high-energy hadronic processes. While well-observed in solar flares, its diffuse cosmic counterpart remains undetected due to strong instrumental backgrounds. Recent studies suggest a correlation between 2.223 MeV emission and the 511 keV electron-positron annihilation line. Since the spatial distribution of Galactic positron sources remains ambiguous, mapping the hadronic 2.223 MeV line could provide the missing key to the decades-old "Positron Puzzle". Using 22 years of legacy data from INTEGRAL/SPI, this project aims to construct a comprehensive background model and an all-sky map of the 2.223 MeV line. By modeling both diffuse Galactic emission and localized point-like hotspots, such as Globular Clusters (GCs) and accreting X-ray binaries, we will determine the luminosity ratios of 511 keV to 2.223 MeV across different astrophysical populations. This rigorous background and signal modeling serves as preparatory work for the upcoming COSI mission, which will offer significantly improved imaging and spectral sensitivity. Mapping the 2.223 MeV line allows us to trace standard hadronic cosmic-ray interactions in the interstellar medium. Comparing its morphology to that of the 511 keV emission, known for its anomalously high bulge-to-disk flux ratio of ~1, will test competing models of positron production. A morphological match would point towards exotic cosmic-ray propagation or localized sources, like stellar flares, whereas a significant mismatch would severely constrain standard astrophysical models, leaving Dark Matter annihilation in the Galactic Bulge as a compelling alternative.