Evolution of and High‐Energy Emission from GHz‐Peaked Spectrum Sources

Abstract

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 -2instruments. In particular, we suggest that GPS radio galaxies should constitute a relatively numerous class of extragalactic sources detected by GLAST.

Radio properties of the γ ‐ray emitting CSO candidate 2234+282

“…Some other models have been investigated to interpret the γ-ray radiation from CSOs. For example, Stawarz et al (2008) proposed that the relativistic electrons injected from the hot spots to the CSO lobes can up-scatter the ultraviolet photons from the disk to GeV energy range. Migliori et al (2014) proposed a two-zone SSC jet model for the γ-ray emission from GPS and CSS quasars, in which the seed synchrotron photons which are from an inner blazar-like jet knot are upscattered by the electrons in an outer slower jet knot.…”

“…The model predicts γ-ray emission from CSOs that could be detected by Fermi, since the electron density and temperature are much higher in the young radio lobes than those in older ones. The difference of these models is that the first two (Migliori et al, 2014;Stawarz et al, 2008) are of nonwww.an-journal.org thermal origin and and the last one (Kino et al, 2009) is thermal. The observational properties of 2234+282 make it a γ-ray CSO candidate, increasing the number of γ-ray CSO candidates from 2 to 3.…”

“…as young radio galaxies (reviewed by Fanti, 2009;O'Dea, 1998). Theoretical models have predicted γ-ray emission from CSOs (Kino et al, 2009;Migliori et al, 2014;Stawarz et al, 2008). However there are only two γ-ray CSO candidates known to date, 4C +55.17 (McConville et al, 2011) and PMN J1603−4904 (Müller et al, 2014).…”

IGM heating in fossil galaxy groups

“…With a faint source detected at 610 MHz for this source, we obtain a positive spectral index of α = +0.93. Positive spectral index is usually observed in GHz Peak spectrum sources (GPS) (Stawarz et al 2008) or compact steep spectrum sources (CSS) and there are two possible explanations of the observed spectral index, the synchrotron self-absorption and the free-free absorption.…”

The Fermi ‐LAT view of young radio sources

“…Other classes of AGN may be able to emit up to the γ-ray energy range, and therefore to be detected by Fermi-LAT (e.g., the Circinus galaxy; Hayashida et al 2013). In particular, young radio sources were predicted to constitute a relatively numerous class of extragalactic objects detectable by Fermi-LAT (Stawarz et al 2008).…”