The relationship between FR0 radio galaxies and gigahertz-peaked spectrum sources

We present the results of our study of the relationship between Fanaroff-Riley type 0 (FR0) radio galaxies and gigahertz-peaked spectrum (GPS) sources. Quasi-simultaneous radio spectra of 34 FR0s were obtained at 2.25-22.3 GHz with the radio telescope RATAN-600 in 2020-2021 during 2-6 epochs. Most FR0s have flat radio spectra, but we found many spectra with a peaked shape. Due to this fact and the compact nature of FR0s, we suggest their possible relationship with compact steep-spectrum (CSS)/GPS radio sources. We analyzed broadband radio spectra of the 34 FR0s using the RATAN-600 measurements and available literature data. There are 14 FR0 objects which can be CSS/GPS radio source candidates. Most FR0s have broader radio spectra than those of genuine GPS sources, with FWHM>2 like in blazars. Most spectral indices at the frequencies below and above the peak do not correspond to the values typical of canonical GPS sources. We classified 3 FR0s as low-power GPS sources according to the canonical criteria. The key issue is the variability properties of FR0s. Some FR0s demonstrate a variability level of up to 25% on a time scale of 1 year according to the RATAN-600 measurements. The flare phenomena in FR0 objects can imply a relationship between them and blazars.

Automated summary

This study examines the relationship between FR0 radio galaxies and GPS sources, suggesting a potential connection between them. Analysis of radio spectra indicates that most FR0 objects have broader spectra than genuine GPS sources, with some demonstrating significant variability. The findings suggest a possible link between FR0 objects and blazars.