Positron Annihilation in the Nuclear Outflows of the Milky Way

Abstract

Observations of soft gamma rays emanating from the Milky Way from SPI/\textit{INTEGRAL} reveal the annihilation of $\sim 2\times 10^{43}$ positrons every second in the Galactic bulge. The origin of these positrons, which annihilate to produce a prominent emission line centered at 511 keV, has remained mysterious since their discovery almost 50 years ago. A plausible origin for the positrons is in association with the intense star formation ongoing in the Galactic center. Moreover, there is strong evidence for a nuclear outflow in the Milky Way. We find that advective transport and subsequent annihilation of positrons in such an outflow cannot simultaneously replicate the observed morphology of positron annihilation in the Galactic bulge and satisfy the requirement that $90$ per cent of positrons annihilate once the outflow has cooled to $10^4\mathrm{K}$.

5 pages, 1 figure. Accepted for publication in Monthly Notices of the Royal Astronomical Society Letters

References in corpus (6)

• Astrophysics Source Code Library
• Giant Gamma-ray Bubbles from Fermi-LAT: AGN Activity or Bipolar Galactic Wind?
• Exciting Dark Matter and the INTEGRAL/SPI 511 keV signal
• The Fermi Bubbles: Giant, Multi-Billion-Year-Old Reservoirs of Galactic Center Cosmic Rays
• The Galactic Positron Annihilation Radiation & The Propagation of Positrons in the Interstellar Medium
• Annihilation Emission from the Galactic Black Hole

Cited by in corpus (6)

• The Positron Puzzle
• Scalar Dark Matter Candidates -- Revisited
• Extinct radio pulsars as a source of subrelativistic positrons
• Detection of positron in-flight annihilation from the Galaxy
• Measuring the smearing of the Galactic 511 keV signal: positron propagation or supernova kicks?
• Updated Constraints on the Injection Energy of Positrons Generating the Galactic 511 keV $\gamma$-ray line