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  • Urquhart, Ryan; Bahramian, Arash; Strader, Jay; Chomiuk, Laura; Ransom, Scott M; Wang, Yuankun; Heinke, Craig O; Tudor, Vlad; Miller-Jones, James C A; Tetarenko, Alexandra J; Maccarone, Thomas J; Sivakoff, Gregory R; Shishkovsky, Laura; Swihart, Samuel J; Tremou, Evangelia

    arXiv.org, 09/2020
    Paper, Journal Article

    Owing to its massive, dense core, Terzan 5 has the richest population of millisecond pulsars known among Galactic globular clusters. Here we report new deep \(2-8\,\)GHz radio continuum observations of Terzan\,5 obtained with the Karl G. Jansky Very Large Array. We have identified a total of 24 sources within the cluster half-light radius, including 17 within the core radius. 19 are associated with previously studied millisecond pulsars and X-ray binaries. Three of the new radio sources have steep radio spectra and are located within the cluster core, as expected for millisecond pulsars. These three sources have hard X-ray photon indices (\(\Gamma=1.3-1.5\)) and highly variable X-ray emission, suggesting they are binary millisecond pulsars belonging to the spider class. For the most X-ray luminous of these sources, the redback spider classification is confirmed by its X-ray light curve, which shows an orbital period of 12.32 hr and double peaked structure around X-ray maximum. The likely discovery of bright binary millisecond pulsars in a well-studied cluster like Terzan 5 highlights how deep radio continuum imaging can complement pulsar search and timing observations in finding probable eclipsing systems. The other new radio source in the core has a flat radio spectrum and is X-ray faint (\(L_X \approx 2\times 10^{31}\) erg s\(^{-1}\)) with a photon index \(\Gamma=2.1\pm0.5\), consistent with the properties expected for a quiescent stellar-mass black hole X-ray binary.