All-sky image from INTEGRAL/SPI
This image shows the entire sky at hard X-ray energies, between 50 and 100 keV, as observed with the Spectrometer on board INTEGRAL (SPI). The image is based on six years worth of data collected with this instrument.
The two main contributions to the emission at these energies are clearly visible: point sources, galactic and extragalactic alike, and diffuse emission. Point sources are scattered across the sky, albeit mainly concentrated along the Galactic Plane; the diffuse emission also traces the Galactic Plane and is fainter, at these energies, than the emission arising from point sources.
In order to study the diffuse emission in great detail and to break it down into the individual physical processes that contribute to it, astronomers need to carefully scrutinise the data and remove the contamination due to point sources.