The discovery of astrophysical neutrino signal by IceCube neutrino telescope has extended the energy frontier of astronomy into Peta-electronvolt energy range. The nature of astronomical sources  is currently uncertain. A breakthrough toward understanding of the nature of these sources can be achieved via detection of the gamma-ray counterpart of the astrophysical neutrino signal. Gamma-ray signal at 100 TeV is now detectable by the HAWC, Tibet and LHAASO telescopes. Further powerful observational facilities, like CTA and SWGO telescopes are under construction or planned.  The subject of the Master  and Thesis work analysis and interpretation of new multi-messenger gamma-ray and neutrino astronomical data at the 100 TeV energy frontier of astronomy and modelling of astronomical sources responsible for these multi-messenger signals. The goal is to understand the nature of cosmic particle accelerators in astronomical objects in the Milky Way and other galaxies.