Detection prospects of Very and Ultra High-Energy gamma rays from extended sources with ASTRI, CTA, and LHAASO

Context. The recent discovery of several ultra high-energy gamma-ray emitters in our Galaxy constitutes a significant advancement towards unveiling its most powerful accelerators and their properties. Nonetheless, in order to unambiguously locate the regions where the highest energy particles are produced and understand the responsible physical mechanisms, detailed spectral and morphological studies are required, especially given that most of the observed sources were found to be significantly extended. Aims. In these regards, pointing observations with the next-generation Imaging Atmospheric Cherenkov Telescopes, like the Cherenkov Telescope Array (CTA) Observatory and the ASTRI Mini-Array (ASTRI), are expected to provide significant improvements. Here we aim at identifying the most promising sources to target in future observations. Methods. To this purpose, we performed a comparative analysis of the expected performance of ASTRI and CTA, computing their differential sensitivities towards extended sources, and further explored their capabilities with respect to specific case studies, including follow-ups of existing gamma-ray source catalogs. Results. We find that almost all of the sources so far detected by LHAASO-WCDA and HGPS will be in the reach of ASTRI and CTA with 300 and 50 hours of exposure, respectively. For the highest energy emitters detected by LHAASO-KM2A, in turn, we provide the list of the most promising objects to be investigated. We further examined specific classes of sources in order to identify potentially detectable gamma-ray emitters, such as passive molecular clouds (i.e. illuminated by the cosmic-ray sea) and pulsars surrounded by a halo of runaway particles.