The connection between radio and high energy emission in black hole powered systems in the SKA era

Abstract

100 MeV gamma-ray energy flux in blazars revealed by the Fermi Gamma-ray Space Telescope. However, there are central issues that need to be clarified in this field: what are the counterparts of the about 30% of gamma-ray sources that are as yet unidentified Are they just blazars in disguise or they are something more exotic, possibly associated with dark matter How would they fit in the radio-gamma ray connection studied so far the radio-gamma ray connection, given that most gamma-ray sources are highly variable With their superb sensitivity, SKA1-MID and SKA1-SUR will help to resolve all of these questions. Even more, while the radio-MeV/GeV connection has been firmly established, a radio-VHE (Very High Energy, E >0:1 TeV) connection has been entirely elusive so far. The advent of CTA (Cherenkov Telescope Array) in the next few years and the expected CTA-SKA1 synergy will offer the chance to explore this connection, even more intriguing as it involves the opposite ends of the electromagnetic spectrum and the acceleration of particles up to the highest energies. We are already preparing to address these questions by exploiting data from the various SKA pathfinders and precursors. We have obtained 18 cm European VLBI Network observations of E > 10 GeV sources, with a detection rate of 83% (and higher than 50% for the unidentified sources). Moreover, we are cross correlating the Fermi catalogs with the Murchinson Widefield Array commissioning survey: when faint gammaray sources are considered, pure positional coincidence is not significant enough for selecting counterparts and we need an additional physical criterion to pinpoint the right object. It can be radio spectral index, variability, polarization, or compactness, needing high angular resolution in SKA1-MID; timing studies can also reveal pulsars, which are often found from dedicated searches of unidentified gamma-ray sources. SKA will be the ideal instrument for investigating these characteristics in conjunction with CTA. A proper classification of the unidentified gammaray sources and the study of the radio-gamma ray connection will be essential to constrain the processes at work in the vicinity of super massive black holes.