Measuring the smearing of the Galactic 511 keV signal: positron propagation or supernova kicks?

Abstract

We use 15 years of $\gamma$-ray data from INTEGRAL/SPI in a refined investigation of the morphology of the Galactic bulge positron annihilation signal. Our spatial analysis confirms that the signal traces the old stellar population in the bulge and reveals for the first time that it traces the boxy bulge and nuclear stellar bulge. Using a 3D smoothing kernel, we find that the signal is smeared out over a characteristic length scale of $150\pm 50$pc, suggesting either annihilation in situ at astrophysical sources kicked at formation or positron propagation away from sources. The former is disfavoured by its requiring kick velocities different between the Galactic nucleus ($\gtrsim 50\mathrm{km}{\mathrm{s}}^{-1}$) and wider bulge ($\lesssim 15\mathrm{km}{\mathrm{s}}^{-1}$) source. Positron propagation prior to annihilation can explain the overall phenomenology of the 511 keV signal for positrons injection energies $\lesssim 1.4$MeV, suggesting a nucleosynthesis origin.

arXiv comment5 pages, 4 figures, 2 tables; submitted with MNRAS Letters

References in corpus (52)

• A Universal Density Profile from Hierarchical Clustering
• Cosmic-ray propagation and interactions in the Galaxy
• Giant Gamma-ray Bubbles from Fermi-LAT: AGN Activity or Bipolar Galactic Wind?
• The Interstellar Environment of our Galaxy
• Radioactive 26Al and massive stars in the Galaxy
• Fermi-LAT Observations of the Diffuse Gamma-Ray Emission: Implications for Cosmic Rays and the Interstellar Medium
• The Nuclear Bulge of the Galaxy. III. Large-Scale Physical Characteristics of Stars and Interstellar Matter
• MeV Dark Matter: Has It Been Detected?
• Exciting Dark Matter and the INTEGRAL/SPI 511 keV signal
• The all-sky distribution of 511 keV electron-positron annihilation emission
• COBE's Galactic Bar and Disk
• The 511 keV emission from positron annihilation in the Galaxy
• Global cosmic-ray related luminosity and energy budget of the Milky Way
• The Fermi Bubbles: Giant, Multi-Billion-Year-Old Reservoirs of Galactic Center Cosmic Rays
• Stringent Constraint on Galactic Positron Production
• Spectral analysis of the Galactic e+e- annihilation emission
• Positron annihilation spectrum from the Galactic Center region observed by SPI/INTEGRAL
• A lower limit of 50 microgauss for the magnetic field near the Galactic Centre
• Gamma-ray spectroscopy of Positron Annihilation in the Milky Way
• Galactic Bulge Preferred Over Dark Matter for the Galactic Center Gamma-Ray Excess
• Evolution towards and beyond accretion-induced collapse of massive white dwarfs and formation of millisecond pulsars
• Hard X-ray emission lines from the decay of Ti-44 in the remnant of supernova 1987A
• The distribution of radioactive ${}^{44}$Ti in Cassiopeia A
• Gamma-ray continuum emission from the inner Galactic region as observed with INTEGRAL/SPI
• The Fermi-LAT GeV Excess Traces Stellar Mass in the Galactic Bulge
• The sky distribution of positronium annihilation continuum emission measured with SPI/INTEGRAL
• The X-shaped Bulge of the Milky Way revealed by WISE
• The lives and deaths of positrons in the interstellar medium
• The Galactic Positron Annihilation Radiation & The Propagation of Positrons in the Interstellar Medium
• Positron annihilation signatures associated with the outburst of the microquasar V404 Cygni
• Interstellar magnetic fields in the Galactic center region
• Diffuse emission measurement with INTEGRAL/SPI as indirect probe of cosmic-ray electrons and positrons
• SN2014J gamma-rays from the 56Ni decay chain
• Continuum gamma-ray emission from light dark matter positrons and electrons
• Positron transport in the interstellar medium
• Positron annihilation spectrum from the Galactic Centre region observed by SPI/INTEGRAL, revisited: annihilation in a cooling ISM?
• Gamma-rays from Type Ia supernova SN2014J
• On the intensity and spatial morphology of the 511 keV emission in the Milky Way
• INTEGRAL/SPI $\gamma$-ray line spectroscopy
• Revisiting INTEGRAL/SPI observations of 44Ti from Cassiopeia A
• Search for 511 keV Emission in Satellite Galaxies of the Milky Way with INTEGRAL/SPI
• Diffuse Galactic antimatter from faint thermonuclear supernovae in old stellar populations
• Monte Carlo modelling of the propagation and annihilation of nucleosynthesis positrons in the Galaxy
• Galactic Binaries Can Explain the Fermi Galactic Center Excess and 511 keV Emission
• ${}^{44}\mathrm{Ti}$ ejecta in young supernova remnants
• Background modelling for $\gamma$-ray spectroscopy with INTEGRAL/SPI
• Constraints on positron annihilation kinematics in the inner Galaxy
• Evidence for a high-energy tail in the gamma-ray spectra of globular clusters
• Comparing simulated ${}^{26}$Al maps to gamma-ray measurements
• Galactic annihilation emission from nucleosynthesis positrons
• Positron Annihilation in the Nuclear Outflows of the Milky Way
• The effect of positron-alkali metal atom interactions in the diffuse ISM