On the Evolution of and High-Energy Emission from GHz-Peaked-Spectrum Sources

Here we discuss evolution and broad-band emission of compact (< kpc) lobes in young radio sources. We propose a simple dynamical description for these objects, consisting of a relativistic jet propagating into a uniform gaseous medium in the central parts of an elliptical host. In the framework of the proposed model, we follow the evolution of ultrarelativistic electrons injected from a terminal hotspot of a jet to expanding lobes, taking into account their adiabatic energy losses as well as radiative cooling. This allows us to discuss the broad-band lobe emission of young radio sources. In particular, we argue that the observed spectral turnover in the radio synchrotron spectra of these objects cannot originate from the synchrotron self-absorption process but is most likely due to free-free absorption effects connected with neutral clouds of interstellar medium engulfed by the expanding lobes and photoionized by active centers. We also find a relatively strong and complex high-energy emission component produced by inverse-Compton up-scattering of various surrounding photon fields by the lobes’ electrons. We argue that such high energy radiation is strong enough to account for several observed properties of GHz-peaked-spectrum (GPS) radio galaxies at UV and X-ray frequencies. In addition, this emission is expected to extend up to GeV (or possibly even TeV) photon energies and can thus be probed by several modern γ-ray Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, Stanford CA 94305 Astronomical Observatory, Jagiellonian University, ul. Orla 171, 30-244 Kraków, Poland Dipartimento di Fisica Generale ‘Amedeo Avogadro’, Università degli Studi di Torino, Via P. Giuria 1, 10125, Torino, Italy Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Torino, Via P. Giuria 1, 10125 Torino, Italy Joint Institute for Laboratory Astrophysics, University of Colorado, Boulder, CO 80309-0440, USA Nicolaus Copernicus Astronomical Center, Bartycka 18, 00-716 Warsaw, Poland Department of Physics, Tokyo Institute of Technology, 2-12-1, Ohokayama, Meguro, Tokyo 152-8551, Japan Landessternwarte Heidelberg, Königstuhl, and Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, Heidelberg 69117, Germany