Gamma-ray spectroscopy of Positron Annihilation in the Milky Way

Abstract

The annihilation of positrons in the Galaxy's interstellar medium produces characteristic gamma-rays with a line at 511 keV. This emission has been observed with the spectrometer SPI on INTEGRAL, confirming a puzzling morphology with bright emission from an extended bulge-like region, and faint disk emission. Most plausible sources of positrons are believed to be distributed throughout the disk of the Galaxy. We aim to constrain characteristic spectral shapes for different spatial components in the disk and bulge with the high-resolution gamma-ray spectrometer SPI, based on a new instrumental background method and detailed multi-component sky model fitting. We confirm the detection of the main extended components of characteristic annihilation gamma-ray signatures at 58$\sigma$ significance in the line. The total Galactic line intensity amounts to $(2.7\pm 0.3)\times 10^{-3}\mathrm{ph}\mathrm{c}{\mathrm{m}}^{-2}{\mathrm{s}}^{-1}$ for our assumed spatial model. We derive spectra for the bulge and disk, and a central point-like and at the position of Sgr A*, and discuss spectral differences. The bulge shows a 511 keV line intensity of $(0.96\pm 0.07)\times 10^{-3}\mathrm{ph}\mathrm{c}{\mathrm{m}}^{-2}{\mathrm{s}}^{-1}$ and an ortho-positronium continuum equivalent to a positronium fraction of ($1.08\pm 0.03$). The 2D-Gaussian representing the disk has an extent of $60_{-5}^{+10}$ deg in longitude and a latitudinal extent of $10.5_{-1.5}^{+2.5}$ deg; the line intensity is $(1.7\pm 0.4)\times 10^{-3}\mathrm{ph}\mathrm{c}{\mathrm{m}}^{-2}{\mathrm{s}}^{-1}$ with a marginal detection of ortho-positronium and an overall diffuse Galactic continuum of $(5.85\pm 1.05)\times 10^{-5}\mathrm{ph}\mathrm{c}{\mathrm{m}}^{-2}{\mathrm{s}}^{-1}\mathrm{ke}{\mathrm{V}}^{-1}$ at 511 keV. The disk shows no flux asymmetry between positive and negative longitudes, although spectral details differ. The flux ratio between bulge and disk is ($0.6\pm 0.1$). The central source has an intensity of $(0.8\pm 0.2)\times 10^{-4}\mathrm{ph}\mathrm{c}{\mathrm{m}}^{-2}{\mathrm{s}}^{-1}$.

16 pages, 29 figures, 10 tables, accepted in A&A

References in corpus (14)

• Secluded WIMP Dark Matter
• The Kinematics of the Ultra-Faint Milky Way Satellites: Solving the Missing Satellite Problem
• The Most Dark Matter Dominated Galaxies: Predicted Gamma-ray Signals from the Faintest Milky Way Dwarfs
• Gamma-ray continuum emission from the inner Galactic region as observed with INTEGRAL/SPI
• The Galactic Positron Annihilation Radiation & The Propagation of Positrons in the Interstellar Medium
• Annihilation Emission from the Galactic Black Hole
• The Galactic ${}^{26}$Al emission map as revealed by INTEGRAL/SPI
• Asymmetries in Extragalactic Double Radio Sources: Clues from 3D Simulations of Jet - Disc Interaction
• Microquasars as sources of positron annihilation radiation
• Shocks, Seyferts and the SNR connection: a Chandra observation of the Circinus galaxy
• Is There a Dark Matter Signal in the Galactic Positron Annihilation Radiation?
• On the Origin of the 511 keV Emission in the Galactic Centre
• Searching for annihilation radiation from SN 1006 with SPI on INTEGRAL
• On the 511 keV emission line of positron annihilation in the Milky Way

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