Characteristics of GPS sources in the Planck survey

Two series of 22.2 and 36.8-GHz observations of 43 GHz-Peaked Spectrum (GPS) radio sources from the Planck survey have been carried out using the 22-m radio telescope of the Crimean Astrophysical Observatory in 2014–2015, with the aim of studying the variability of these sources. The interval between the two series of observations was about nine months. These data were analyzed together with the Planck data at frequencies from 20 to 143 GHz. The fraction of quasars among GPS sources grows to 90% at millimeter wavelengths, compared to 1.4% at decimeter wavelengths. The growth in the variability indices of Planck GPS sources is not as sharp as that observed at decimeter and centimeter wavelengths, and remains at a level of about 30% at millimeter wavelengths. This supports the view that GPS sources are not strongly variable, compared to other types of Active Galactic Nuclei (AGNs). A mean spectrumfor the GPS radio sources has been obtained, which is shallower at low frequencies and steeper at high frequencies atmillimeter wavelengths than at decimeter and centimeterwavelengths. These properties of the GPS spectra at millimeter wavelengths testify to the compactness of these sources and the dense, inhomogeneous nature of the medium in which they are located. This also indirectly suggests that these objects are young and that their active states have short lifetimes.