X-ray background radiation
X-ray background radiationA diffuse sky background radiation that was one of the first discoveries in X-ray astronomy. It is detected over 4 decades in frequency, and its origin varies across this band; most of the energy in the background is concentrated at 20–40keV. At very low energies the background is from hot gas in a ‘Local Bubble’. In the 0.5–2keV energy band the ROSAT satellite has successfully identified the source as being mostly due to active galaxies at moderate redshift. The ‘hard’ background above 3keV has a different spectrum and is thought to be due to the integrated emission from many heavily absorbed quasars at a range of redshifts.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006