Abstract

Contributed Talk - Splinter Solar

Tuesday, 10 September 2024, 16:00   (S15)

Contribution of stellar flares to the 511 keV emission in the Galaxy

Saurabh Mittal, Thomas Siegert
Lehrstuhl für Astronomie, Universität Würzburg

Observations of the 511 keV signal in the Galaxy, resulting from positron annihilation, 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 of the leading scenarios is positron production in stellar flares. Previous studies have detected the 511 keV line from high energy Solar flares (1e34 erg). Given that other stars flare in a similar manner as the Sun, stellar flares can be considered as contributing positron sources. Furthermore, pico- and nano-flares (1e22 - 1e24 erg) might have an even larger cumulative contribution due to their higher frequency. Also, the INTEGRAL/SPI 511 keV sky can be statistically described using old stellar population further strengthening this idea. To investigate this scenario quantitatively, first we analyzed data from several instruments to obtain a relation between the 511 keV line luminosity and the flare energy in the Sun. Due to the lack of direct measurements, this correlation was obtained using multiple sub-correlations derived from different instruments. This quasi-persistent 511 keV flux of the Sun can then be extended to population of stars, such as in globular clusters resulting in the total 511 keV flux prediction from stellar flares. The expected cumulative flux from all globular clusters of the Milky Way suggests that flaring stars alone cannot sufficiently explain the 511 keV emission in the Galaxy. Stellar flares might contribute significantly to this emission if the maximum flare energy of stars was 1e55 erg, or if the positrons escaping from flare events was on the order of 1e9.