A complete sample of LSP blazars fully described in gamma-rays. New gamma-ray detections and associations with Fermi-LAT

Context. We study the gamma-ray and broadband spectral energy distribution (SED) properties of a complete sample of 104 bright, radio-selected low-synchrotron peaked (LSP) blazars, which have well-characterized SEDs from radio to X-rays. Most of the sources have already been detected in the gamma-ray band by Fermi-LAT, however almost 20% of these blazars have no counterpart in any of the Fermi catalogs published so far. <BR /> Aims Using the Fermi Science Tools, we look for gamma-ray emission for those objects not yet reported in any Fermi-LAT catalog, finding new detections and associations. We then study the multifrequency SED for all sources in our sample, fitting their synchrotron (Syn) and inverse Compton (IC) components. A complete sample of LSP blazars with a full description in gamma-ray is unique. We use this sample to derive the distribution of the Compton dominance (CD) along with population properties such as Syn and IC peak power, and frequency distributions. <BR /> Methods We performed a binned likelihood analysis in the 0.3-500 GeV energy band with Fermi-LAT Pass 8 data, integrating over 7.5 yr of observations. We studied gamma-ray light curves and test statistic (TS) maps to validate new detections and associations, thereby building a better picture of the high-energy activity in radio-selected LSP blazars. We fit the IC component for the new detections using all data at our disposal from X-rays to GeV gamma-rays, enhancing the amount of information available to study the Syn to IC peak-power correlations. <BR /> Results We deliver a unique characterization in gamma-rays for a complete sample of LSP blazars. We show that three previously unidentified 3FGL sources can be associated with blazars when using improved gamma-ray positions obtained from TS maps. Six previously unreported gamma-ray sources are detected at TS > 20 level, while another three show TS values between 10-20. We evaluate two cases in which source confusion is likely present. In four cases there is no significant gamma-ray signature when integrating over 7.5 yr. Short-lived flares at 1 month scale, however, have been detected in these sources. Finally, we measure the log(CD) for the sample, which has a Gaussian-like distribution with median log(CD) ≈ 0.1, implying that on average the peak-power for the Syn and IC components in LSP blazars is similar.