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

Abstract

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. 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 so far. Using the Fermi Science Tools, we look for $\gamma$-ray emission for those objects not yet reported in any Fermi-LAT catalog. We performed a binned likelihood analysis in the 0.3-500 GeV energy band with Fermi-LAT Pass 8 data, integrating over 7.5 years of observations. We studied $\gamma$-ray light curves and test statistic (TS) maps to validate new detections and associations. We fit the synchrotron (Syn) and inverse Compton (IC) components for all sources using all available historical data, enhancing the study of Syn to IC peak-power correlations. We derive the distribution of the Compton dominance (CD) along with population properties such as Syn and IC peak power, and frequency distributions. 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, however short-lived flares have been detected in these sources. Finally, the log(CD) 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 are similar.Comment: 19 pages, 24 figures, Accepted for publication in A&