Initial stages of black hole activity probed with X-rays from young extragalactic radio sources

There is growing evidence that the onset of black hole (BH) activity is accompanied by a formation of a radio jet. Jet's impact on BH surrounding and further BH feeding are believed to be essential to the AGN-galaxy feedback idea. Highly relativistic plasma contained within young radio lobes and shocks due to jet expansion are expected to generate high energy radiation. However, observing young radio jets at high energies has been challenging as they proved to be relatively faint. Here we discuss the most recent results for the four Compact Symmetric Objects (CSO; radio structure sizes 2-16 pc, ages 100-400 years) based on the new high quality broad-band radio-to-gamma-ray spectral energy distributions including Chandra, XMM-Newton (AO17), NuSTAR (AO4) and Fermi/LAT data. For the first time, we have now means to test theoretical scenarios for the high energy emission of the youngest radio jets (radio lobes origin, shocked ISM, jet, disk corona). We were able to refute the radio lobes origin in at least one source, confirm the Compton thick nature of CSO J1511+0518, and collect evidence that PKS 1843+356 is most likely a blazar and not a CSO. These findings provide further evidence in favor of the Compton thick/thin dichotomy of the CSO environment that we have recently discovered. This dichotomy may suggest that X-ray obscured CSOs have smaller radio sizes than X-ray unobscured CSOs with the same radio power, and indicate that the environment may play a crucial role in regulating the early growth of the radio jets. Importantly, X-ray properties of the Compton thick CSO sub-population, in conjunction with recent developments in the optical/IR and radio bands, offer new insight for understanding the structure and size of the AGN obscuring torus, as they probe the X-ray emission/absorption/scattering features on the torus (parsec) scale. We discuss the implications of our results for the high energy emission models of radio jets, the earliest stages of the radio source evolution, diversity of the medium in which the jets expand, and jet-galaxy co-evolution.