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Early SPI/INTEGRAL measurements of galactic 511 keV line emission from positron annihilation

P. Jean, J. Knoedlseder, V. Lonjou, M. Allain, J. -P. Roques, G. K. Skinner, B. J. Teegarden, G. Vedrenne, P. von Ballmoos, B. Cordier, P. Caraveo, R. Diehl, Ph. Durouchoux, P. Mandrou, J. Matteson, N. Gehrels, V. Schoenfelder, A. W. Strong, P. Ubertini, G. Weidenspointner, C. Winkler

TL;DR

This paper presents the first high-resolution spectroscopic measurements of the Galactic Center 511 keV line with INTEGRAL/SPI. An extensive dataset from GCDE and GPS in 2003 is analyzed with a two-component instrumental background model and likelihood fits to various spatial distributions, yielding a line flux of on the order of $10^{-4}$ ph cm$^{-2}$ s$^{-1}$, a centroid near the rest energy, and an intrinsic width at the upper end of prior measurements. The emission appears extended rather than point-like, with a best-fitting Gaussian FWHM around $10^ rac{\circ}{ }$ and a 2σ lower limit of $6^ rac{\circ}{ }$, aligning with previous results but challenging compact-source scenarios. These findings have implications for the environments and processes responsible for positron production and annihilation in the Galaxy and demonstrate SPI’s capability for detailed GC studies.

Abstract

We report the first measurements of the 511 keV line emission from the Galactic Centre (GC) region performed with the spectrometer SPI on the space observatory INTEGRAL (International Gamma-Ray Astrophysics Laboratory). Taking into account the range of spatial distribution models which are consistent with the data, we derive a flux of $9.9^{+4.7}_{-2.1} \times 10^{-4}$ ph cm$^{-2}$ s$^{-1}$ and an intrinsic line width of $2.95^{+0.45}_{-0.51}$ keV (FWHM). The results are consistent with other high-spectroscopy measurements, though the width is found to be at the upper bound of previously reported values.

Early SPI/INTEGRAL measurements of galactic 511 keV line emission from positron annihilation

TL;DR

This paper presents the first high-resolution spectroscopic measurements of the Galactic Center 511 keV line with INTEGRAL/SPI. An extensive dataset from GCDE and GPS in 2003 is analyzed with a two-component instrumental background model and likelihood fits to various spatial distributions, yielding a line flux of on the order of ph cm s, a centroid near the rest energy, and an intrinsic width at the upper end of prior measurements. The emission appears extended rather than point-like, with a best-fitting Gaussian FWHM around and a 2σ lower limit of , aligning with previous results but challenging compact-source scenarios. These findings have implications for the environments and processes responsible for positron production and annihilation in the Galaxy and demonstrate SPI’s capability for detailed GC studies.

Abstract

We report the first measurements of the 511 keV line emission from the Galactic Centre (GC) region performed with the spectrometer SPI on the space observatory INTEGRAL (International Gamma-Ray Astrophysics Laboratory). Taking into account the range of spatial distribution models which are consistent with the data, we derive a flux of ph cm s and an intrinsic line width of keV (FWHM). The results are consistent with other high-spectroscopy measurements, though the width is found to be at the upper bound of previously reported values.

Paper Structure

This paper contains 4 sections, 3 equations, 3 figures, 1 table.

Table of Contents

  1. Introduction
  2. Data analysis
  3. Results
  4. Conclusions

Figures (3)

  • Figure 1: Raw spectrum and background model components.
  • Figure 2: Rate induced by galactic 511 keV photons as a function of longitude. The response to a gaussian source (FWHM = 10$^\circ$) is also shown for comparison.
  • Figure 3: 511 keV flux spectrum obtained using a gaussian centred on the GC with a FWHM of 10$^\circ$.