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2008ApJ...679.1315B - Astrophys. J., 679, 1315-1326 (2008/June-1)

INTEGRAL SPI all-sky view in soft gamma rays: a study of point-source and galactic diffuse emission.

BOUCHET L., JOURDAIN E., ROQUES J.-P., STRONG A., DIEHL R., LEBRUN F. and TERRIER R.

Abstract (from CDS):

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°x∼10°, potentially associated with the disk or halo surrounding the central regions of our Galaxy.