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For around forty years, astrophysicists have observed the annihilation of positrons in the Galaxy at a prodigious rate. Around 2 x 10^43 positrons annihilate every second, giving rise to diffuse emission of soft 511 keV gamma rays, which have been mapped most recently by the SPI spectrometer on board ESAтАЩs INTEGRAL satellite observatory. Despite years of study and the ubiquity of positron annihilation in astrophysical environments, these long-standing observations are hard to explain. The fact the Galactic bulge far outshines the disk in annihilating positrons which are injected into the ISM at low energies makes the source of the positrons difficult to identify, as the main source of such positrons are prima facie located in the Galactic disk. I will present my PhD thesis proposal: An ancient stellar source of the Galactic bulge positron excess, and describe the work we intend to carry out to investigate the plausibility of the positrons originating in sub-luminous supernovae associated with the ancient stars of the Galactic bulge. |
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