科研之友
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摘要
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.
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.
Methods. We performed a binned likelihood analysis in the 0.3-500GeV 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.
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 similar to 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) approximate to 0.1, implying that on average the peak-power for the Syn and IC components in LSP blazars is similar.
- 出版日期2018-8-7
