Monte Carlo modelling of the propagation and annihilation of nucleosynthesis positrons in the Galaxy

Abstract

We want to estimate whether the positrons produced by the beta plus decay of 26Al, 44Ti and 56Ni synthesised in massive stars and supernovae are sufficient to explain the 511 keV annihilation emission observed in our Galaxy. Such a possibility has often been put forward in the past. We developed a Monte Carlo Galactic propagation code for ~MeV positrons in which the Galactic interstellar medium, the Galactic magnetic field (GMF) and the propagation are finely described. This code allows us to simulate the spatial distribution of the 511 keV annihilation emission. We test several GMFs models and several positron escape fractions from type-Ia supernova for 56Ni positrons. We consider the collisional ballistic transport mode and then compare the simulated 511 keV intensity spatial distributions to the INTEGRAL/SPI data. Whatever the GMF configuration and the escape fraction chosen for 56Ni positrons, the 511 keV intensity distributions are very similar. The main reason is that ~MeV positrons do not propagate very far away from their birth sites in our model. The direct comparison to the data does not allow us to constrain the GMF configuration and the escape fraction for 56Ni positrons. In any case, nucleosynthesis positrons produced in steady state cannot explain the full annihilation emission. The comparison to the data shows that: (a) the annihilation emission from the Galactic disk can be accounted for; (b) the strongly peaked annihilation emission from the inner Galactic bulge can be explained by positrons annihilating in the central molecular zone but this seems to require more positron sources than the population of massive stars and type Ia supernovae usually assumed for this region; (c) the more extended emission from the Galactic bulge cannot be explained. We show that a transient source at the GC, such as a starburst episode, could explain this extended component.

14 pages, 7 figures, accepted for publication in A&A

References in corpus (13)

• Giant Gamma-ray Bubbles from Fermi-LAT: AGN Activity or Bipolar Galactic Wind?
• A New Model of the Galactic Magnetic Field
• Rates and properties of type Ia supernovae as a function of mass and star-formation in their host galaxies
• Radio observational constraints on Galactic 3D-emission models
• Giant Magnetized Outflows from the Centre of the Milky Way
• Spatial distribution of interstellar gas in the innermost 3 kpc of our Galaxy
• The Galactic Positron Annihilation Radiation & The Propagation of Positrons in the Interstellar Medium
• Continuum gamma-ray emission from light dark matter positrons and electrons
• Annihilation Emission from the Galactic Black Hole
• Interstellar gas within $\sim 10$ pc of Sgr A${}^{\ast }$
• Interacting dark matter contribution to the Galactic 511 keV gamma ray emission: constraining the morphology with INTEGRAL/SPI observations
• Diffuse Gamma-ray Emission from the Galactic Center - A Multiple Energy Injection Model
• Galactic annihilation emission from nucleosynthesis positrons

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