The extragalactic gamma sky is dominated by the class of blazars. Blazars are Active Galactic Nuclei (AGN) with a relativistic jet (composed of ionized matter traveling at nearly the speed of light) pointed towards Earth.
Current generation of Cherenkov telescope have been able to detect principally the most extreme blazars. The wide angle survey planned for CTA and ASTRI mini-array will allow a great leap forward, since they will guarantee a more unbiased census of the blazar population. The CTA extragalactic survey will allow the detection of less extreme blazars, while the ASTRI mini-array will permit the detection of extreme high BL Lacs, so far undetected at low energies by Fermi.
Artist's impressionof a Blazar.