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Early SPI/INTEGRAL contraints on the morphology of the 511 keV line emission in the 4th galactic quadrant

J. Knodlseder, V. Lonjou, P. Jean, M. Allain, P. Mandrou, J. -P. Roques, G. K. Skinner, G. Vedrenne, P. von Ballmoos, G. Weidenspointner, P. Caraveo, B. Cordier, V. Schonfelder, B. J. Teegarden

TL;DR

The paper addresses the origin and distribution of Galactic positrons by constraining the morphology of the 511 keV annihilation line using INTEGRAL/SPI observations of the Galactic Centre. It applies imaging with Richardson-Lucy and parametric Gaussian bulge modeling, including careful background treatment, to separate bulge and disk contributions. The results indicate a bulge-dominated emission with a FWHM of about $9°$ and a flux of $9.9^{+4.7}_{-2.1} imes 10^{-4}$ ph cm^{-2} s^{-1}$, while no significant disk component is detected; 2σ upper limits on disk flux are $(1.4-3.4) imes 10^{-3}$ ph cm^{-2} s^{-1}$, yielding bulge-to-disk ratio lower limits of roughly $0.3-0.6$. These findings provide early, quantitative constraints on the Galactic positron morphology, supporting a dominant bulge source and guiding future analyses with larger SPI data sets to refine the disk contribution and source models.

Abstract

We provide first constraints on the morphology of the 511 keV line emission from the galactic centre region on basis of data taken with the spectrometer SPI on the INTEGRAL gamma-ray observatory. The data suggest an azimuthally symmetric galactic bulge component with FWHM of ~9 deg with a 2 sigma uncertainty range covering 6-18 deg. The 511 keV line flux in the bulge component amounts to (9.9+4.7-2.1) 10e-4 ph cm-2 s-1. No evidence for a galactic disk component has been found so far; upper 2 sigma flux limits in the range (1.4-3.4) 10e-3 ph cm-2 s-1 have been obtained that depend on the assumed disk morphology. These limits correspond to lower limits on the bulge-to-disk ratio of 0.3-0.6.

Early SPI/INTEGRAL contraints on the morphology of the 511 keV line emission in the 4th galactic quadrant

TL;DR

The paper addresses the origin and distribution of Galactic positrons by constraining the morphology of the 511 keV annihilation line using INTEGRAL/SPI observations of the Galactic Centre. It applies imaging with Richardson-Lucy and parametric Gaussian bulge modeling, including careful background treatment, to separate bulge and disk contributions. The results indicate a bulge-dominated emission with a FWHM of about and a flux of ph cm^{-2} s^{-1}(1.4-3.4) imes 10^{-3}, yielding bulge-to-disk ratio lower limits of roughly . These findings provide early, quantitative constraints on the Galactic positron morphology, supporting a dominant bulge source and guiding future analyses with larger SPI data sets to refine the disk contribution and source models.

Abstract

We provide first constraints on the morphology of the 511 keV line emission from the galactic centre region on basis of data taken with the spectrometer SPI on the INTEGRAL gamma-ray observatory. The data suggest an azimuthally symmetric galactic bulge component with FWHM of ~9 deg with a 2 sigma uncertainty range covering 6-18 deg. The 511 keV line flux in the bulge component amounts to (9.9+4.7-2.1) 10e-4 ph cm-2 s-1. No evidence for a galactic disk component has been found so far; upper 2 sigma flux limits in the range (1.4-3.4) 10e-3 ph cm-2 s-1 have been obtained that depend on the assumed disk morphology. These limits correspond to lower limits on the bulge-to-disk ratio of 0.3-0.6.

Paper Structure

This paper contains 6 sections, 1 equation, 3 figures.

Table of Contents

  1. Introduction
  2. Data analysis
  3. Imaging
  4. Model fitting
  5. Discussion
  6. Conclusions

Figures (3)

  • Figure 1: Relative exposure map of the galactic centre region. Black corresponds to regions of maximum exposure.
  • Figure 2: 511 keV gamma-ray line intensity map of the galactic centre region (only negative longitudes). Black corresponds to regions of maximum 511 keV line intensity. Longitude and latitude profiles, integrated over $b=\pm5^\circ$ and $l=-5^\circ - 0^\circ$, respectively, are shown as insets.
  • Figure 3: Simulated 511 keV gamma-ray line intensity map based on an azimuthally symmetric gaussian model of 10$^\circ$ FWHM centred at $l=0^\circ$ and $b=0^\circ$.