Origin of the Galactic 511 keV emission from positrons produced in irregular supernovae

Understand

Gamma ray emission of 511 keV lines arising from electron-positron annihilation has been detected from the Galaxy since the 70s.

• Spatially resolved observations using the INTEGRAL satellite have shown its full sky distribution to be strongly concentrated in the Galactic bulge, with a smaller contribution from the disk, unlike the situation in any other wavelength.
• The puzzling distribution of the positrons gave rise to various suggestions, including stellar nucleosynthesis in core-collapse (CC) and type Ia thermonuclear supernovae (SNe), accreting compact objects, and more "exotic" explanations of annihilation of dark-matter particles.
• However, such models encounter difficulties in reproducing the total Galactic 511 keV flux as well as its peculiar bulge-centered distribution.