High energy emission and cosmic accelerators

Active galactic nuclei (AGN) and transients (including exploding/merging stars: supernovae, gamma-ray bursts; star - supermassive black hole encounters in tidal disruption events) host a compact object powered central engine. These natural cosmic accelerators are responsible for the production and proliferation of a broad electromagnetic spectrum (radio - dash; gamma-rays), high energy particles (cosmic rays, neutrinos) and gravitational waves, collectively representing multi-messenger signatures. I will discuss ongoing investigations on the association between blazars (AGN hosting powerful, large scale astrophysical jet pointed towards the observer) and high energy PeV neutrinos. This includes the blazar TXS 0506+056, which has been the subject of intensive observational campaigns. I will then discuss an investigation of a tidal disruption event AT2019dsg, with circumstantial evidence for a PeV neutrino association. In these, high resolution radio very long baseline interferometry observations play an essential role in elucidating the compact central region and its evolution. The modelling of electromagnetic emission from accretion - jet/outflow mechanisms (for neutrino production) will be discussed in the context of conducive physical conditions in these cosmic accelerators.