The Positron Puzzle

Abstract

The Positron Puzzle is a half-century old conundrum about the origin of the Galactic $\gamma$-ray emission line at photon energies of 511 keV, and the shape of its morphology, showing a bulge-to-disk luminosity ratio of $\sim 1$ - unlike any astrophysical source distribution. Positrons that have been cooled to the eV scale capture electrons and form the intermediate bound state of Positronium (Ps) which decays on a nano-second timescale into two or three photons. Assuming the emission to originate from the Galactic bulge, centre, and disk, a visible annihilation rate in the Milky Way of $\sim 5\times 10^{43}{\mathrm{e}}^{+}{\mathrm{s}}^{-1}$ has to be explained, either by a quasi-steady state of production and annihilation, or by possibly multiple burst-like events that flood the Galaxy with positrons, then fading away on a Myr timescale. In this paper, I will review what the real Positron Puzzle is, where data and simulations have been used inadequately which resulted in false claims and an apparent quandary, what we really know and absolutely not know about the topic, and how this epistemic problem might be advancing.

Invited contribution, 27 pages, 8 figures, 2 tables, accepted in Astrophysics and Space Sciences

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Cited by in corpus (12)

• Multimessenger search for electrophilic feebly interacting particles from supernovae
• Anomalous Ionization in the Central Molecular Zone by sub-GeV Dark Matter
• The Morphology of Exciting Dark Matter and the Galactic 511 keV Signal
• Imaging the positron annihilation line with 20 years of INTEGRAL/SPI observations
• Gamma-ray line emission from the Local Bubble
• Production of radioactive ${}^{22}$Na in core-collapse supernovae: the Ne-E(L) component in presolar grains and its possible consequences on supernova observations
• Bottom-up Background Simulations of the 2016 COSI Balloon Flight
• Enhancing Compton telescope imaging with maximum a posteriori estimation: a modified Richardson-Lucy algorithm for the Compton Spectrometer and Imager
• Updated Constraints on the Injection Energy of Positrons Generating the Galactic 511 keV $\gamma$-ray line
• Search for a Non-Relativistic Boson in Two-Body Antimuon Decay
• High Energy Emission from the Galactic Center
• Galactic Electron-Positron Annihilation Emission from X-Ray Binaries with Transient and Persistent Jets