Soft gamma-ray galactic ridge emission as unveiled by SPI aboard INTEGRAL

TL;DR

This study uses SPI aboard INTEGRAL to produce the first detailed all-sky images of soft gamma-ray galactic ridge emission, revealing its morphology and providing insights into its underlying emission processes.

Contribution

First imaging of diffuse and point-like soft gamma-ray emission in the galaxy, clarifying the spatial distribution of the galactic ridge emission.

Findings

Revealed the morphology of the galactic ridge emission.

Distinguished between diffuse and point-like emission components.

Provided constraints on the nature of gamma-ray emission processes.

Abstract

The origin of the soft gamma-ray (200 keV - 1 MeV) galactic ridge emission is one of the long-standing mysteries in the field of high-energy astrophysics. Population studies at lower energies have shown that emission from accreting compact objects gradually recedes in this domain, leaving place to another source of gamma-ray emission that is characterised by a hard power-law spectrum extending from 100 keV up to 100 MeV The nature of this hard component has remained so far elusive, partly due to the lack of sufficiently sensitive imaging telescopes that would be able to unveil the spatial distribution of the emission. The SPI telescope aboard INTEGRAL allows now for the first time the simultaneous imaging of diffuse and point-like emission in the soft gamma-ray regime. We present here all-sky images of the soft gamma-ray continuum emission that clearly reveal the morphology of the different emission components. We discuss the implications of our results on the nature of underlying emission processes and we put our results in perspective of GLAST studies of diffuse galactic continuum emission.