2008/01/14 by L. Bouchet, E. Jourdain, J.‐P. Roques +6 · 1 citation
Physics and Astronomy · #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Astrophysics and Cosmic Phenomena #Galaxies: Formation, Evolution, Phenomena #Gamma ray #Gamma-ray astronomy #Optics #Physics #Point (geometry) #Point source #Sky #Soft X-rays #astro-ph
paper · pdf · doi:10.1086/529489
28 pages, 10 figures. Astrophysical journal (accepted for publication)
arxiv created 2008/01/14 · openalex publication_date 2008/05/30 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We have processed the data accumulated with the INTEGRAL SPI instrument over 4 years (~51 Ms) to study the morphology of the Galactic "diffuse" emission in the 20 keV to 8 MeV energy range. To achieve this, we simultaneously derived an all-sky census of emitting sources and images of the Galactic ridge (GR) emission. In the central radian, the resolved point-source emission amounts to 88%, 91%, and 68% of the total in the 25-50, 50-100, and 100-300 keV domains, respectively. We compare the spatial distribution of the GR emission with the distributions obtained from CO and near-IR maps and quantify our results through latitude and longitude profiles. Below 50 keV, the SPI data are better traced by the latter, supporting a stellar origin for this emission. Furthermore, we find that the GR emission spectrum follows a power law with a photon index ~1.55 above 50 keV, while an additional component is required below that energy. This component shows a cutoff around 30 keV, reinforcing a stellar origin, as proposed by Krivonos et al. The component of the diffuse emission due to e ± annihilations is extracted simultaneously, leading to the determination of the related parameters (positronium flux and fraction). Specific discussion is devoted to the annihilation-line distribution, since significant emission is detected over a region as large as ~80° × ~10°, potentially associated with the disk or halo surrounding the central regions of our Galaxy.