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Stellar Flares to Explain the Galactic 511 keV Emission

Presentation #104.01 in the session ISM/Galaxies - Poster Session.

Published onMay 03, 2024
Stellar Flares to Explain the Galactic 511 keV Emission

Positron annihilation results in a gamma-ray line at 511 keV photon energies. Observations of the 511 keV signal in the Galaxy have shown a diffuse nature with the Galactic bulge being as bright as the disk. The origin of these positrons in the Milky Way and how far they propagate before annihilating has been under discussion for five decades with many different sources and mechanisms being used to explain this phenomenon.One such mechanism is found in stellar flares. Previous studies have detected the 511 keV line from high energy Solar flares (1e34 erg) but pico- and nano-flares (1e21 - 1e24 erg) might have an even larger contribution to this line due to their higher frequency. Other stars flare in a similar manner as the Sun with a similar flare frequency energy distribution. We use data from Fermi/GBM and INTEGRAL/SPI to obtain a relation between the 511 keV line luminosity and the flare energy. This yields a quasi-persistent 511 keV flux of the Sun which can be extended to populations of stars, such as in globular clusters. This model applied to the 157 globular clusters of the Milky Way would account for more than 10% of the total Galactic diffuse flux of 3e-3 ph/cm2/s. Our preliminary estimates suggest that the positron production rates in Solar flares obtained from Bisnovatyi-Kogan and Pozanenko (2017) might have been largely overestimated. The expected cumulative flux from all globular clusters is within reach of the upcoming COSI-SMEX mission, slated for launch in 2027 with a planned duration of 2 years.

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