INTEGRALSPI All‐Sky View in Soft Gamma Rays: A Study of Point‐Source and Galactic Diffuse Emission

Abstract

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 25Y50, 50Y100, and 100Y300 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 AE 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.

Constraining light dark matter with diffuse X-ray and gamma-ray observations

“…The collected normalized dataset of photon fluxes used to place constraints on decaying and annihilating DM in this paper. Data from HEAO-1 [63] (orange), INTEGRAL [64] (green), COMPTEL [65][66][67] (blue), EGRET [68,69] (red), and Fermi [70] (yellow) are shown. All error bars are statistical, except for the EGRET and Fermi datasets, where the dominant systematic uncertainties are shown.…”

“…We use data from observations of 20 keV to 2 MeV photons from the region | | < 30 • and |b| < 15 • obtained with the SPI instrument onboard IN-TEGRAL [64]. The quantity J changes by up to O(30%) in the decaying case, for different choices of density profile.…”

“…To illustrate the improvements possible with using a simultaneous fit of signal and backgrounds, we use the background components as derived by the different collaborations in [63][64][65][66][67][68][69][70] and perform a naïve χ 2 goodness-of-fit test (GOF) in figure 15. For the GOF, we take as many distinct background components as have been identified by each collaboration, and, keeping the slopes fixed, allow the normalizations to float.…”

Integral Status Overview

“…The bulge emission remains symmetric [25].  Deep observations of the galactic ridge emission [26], [27] from the inner radian show that (i) below 50 to 60 keV, accreting white dwarf binaries (CV) dominate the emission which is compatible with the NIR emission at 4.9 µ [26]; (ii) the integrated signal fom point sources dominate the range from 50 keV to ~ 300 keV; (iii) 511 keV line and Ps continuum emission are prominent between 300, and 511 keV; and (iv) a diffuse, hard power-law component emerges at energies above 300 keV. The latter one can be well modeled, together with data from CGRO, by Inverse Compton scattering from relativistic electrons in the ISM, showing that INTEGRAL is a good tracer of GeV electrons and positrons in our Galaxy [28], however, a yet unknown population of sources with hard spectra (Pulsars ?…”

“… A unique observation of the diffuse cosmic X-ray background, using the Earth as an occulting device, determined the CXB at hard X-ray energies with high accuracy [16].  Hard X-ray/soft γ-ray point source catalogues provide important new data on galactic and extragalactic source populations in the 15 keV -8 MeV band [6], [17], [18].  Detection of polarization in the high -energy emission of the Crab pulsar and in the prompt emission of gamma -ray burst GRB 041219A, both with SPI and IBIS [19], [20], [21], [22].…”