VERITAS discovery of very high energy gamma-ray emission from S3 1227+25 and multiwavelength observations
Authors: Atreya Acharyya (VERITAS Collaboration), Colin Adams (VERITAS Collaboration), Avery Archer (VERITAS Collaboration), Priyadarshini Bangale (VERITAS Collaboration), Wystan Benbow (VERITAS Collaboration), Aryeh Brill (VERITAS Collaboration), Jodi Christiansen (VERITAS Collaboration), Alisha Chromey (VERITAS Collaboration), Manel Errando (VERITAS Collaboration), Abe Falcone (VERITAS Collaboration), Qi Feng (VERITAS Collaboration), John Finley (VERITAS Collaboration), Gregory Foote (VERITAS Collaboration), Lucy Fortson (VERITAS Collaboration), Amy Furniss (VERITAS Collaboration), Greg Gallagher (VERITAS Collaboration), William Hanlon (VERITAS Collaboration), David Hanna (VERITAS Collaboration), Olivier Hervet (VERITAS Collaboration), Claire Hinrichs (VERITAS Collaboration), John Hoang (VERITAS Collaboration), Jamie Holder (VERITAS Collaboration), Weidong Jin (VERITAS Collaboration), Madalyn Johnson (VERITAS Collaboration), Philip Kaaret (VERITAS Collaboration), Mary P. Kertzman (VERITAS Collaboration), David Kieda (VERITAS Collaboration), Tobias Kleiner (VERITAS Collaboration), Nikolas Korzoun (VERITAS Collaboration), Frank Krennrich (VERITAS Collaboration), Mark Lang (VERITAS Collaboration), Matthew Lundy (VERITAS Collaboration), Gernot Maier (VERITAS Collaboration), Conor McGrath (VERITAS Collaboration), Matthew Millard (VERITAS Collaboration), John Millis (VERITAS Collaboration), Connor Mooney (VERITAS Collaboration), Patrick Moriarty (VERITAS Collaboration), Reshmi Mukherjee (VERITAS Collaboration), Stephan O'Brien (VERITAS Collaboration), Rene A. Ong (VERITAS Collaboration), Martin Pohl (VERITAS Collaboration), Elisa Pueschel (VERITAS Collaboration), John Quinn (VERITAS Collaboration), Kenneth J. Ragan (VERITAS Collaboration), Paul Reynolds (VERITAS Collaboration), Deivid Ribeiro (VERITAS Collaboration), Emmet Thomas Roache (VERITAS Collaboration), Iftach Sadeh (VERITAS Collaboration), Alberto Sadun (VERITAS Collaboration), Lab Saha (VERITAS Collaboration), Marcos Santander (VERITAS Collaboration), Glenn Sembroski (VERITAS Collaboration), Ruo Shang (VERITAS Collaboration), Megan Splettstoesser (VERITAS Collaboration), Anjana Talluri (VERITAS Collaboration), James Tucci (VERITAS Collaboration), Vladimir Vassiliev (VERITAS Collaboration), David Williams (VERITAS Collaboration), Sam Wong (VERITAS Collaboration), Talvikki Hovatta, Svetlana Jorstad, Sebastian Kiehlmann, Anne Lahteenmaki, Ioannis Liodakis, Alan Marscher, Walter Max-Moerbeck, Anthony Readhead, Rodrigo Reeves, Paul S Smith, Merja Tornikoski
Abstract: We report the detection of very high energy gamma-ray emission from the blazar S3 1227+25 (VER J1230+253) with the Very Energetic Radiation Imaging Telescope Array System (VERITAS). VERITAS observations of the source were triggered by the detection of a hard-spectrum GeV flare on May 15, 2015 with the Fermi-Large Area Telescope (LAT). A combined five-hour VERITAS exposure on May 16th and May 18th resulted in a strong 13$\sigma$ detection with a differential photon spectral index, $\Gamma$ = 3.8 $\pm$ 0.4, and a flux level at 9% of the Crab Nebula above 120 GeV. This also triggered target of opportunity observations with Swift, optical photometry, polarimetry and radio measurements, also presented in this work, in addition to the VERITAS and Fermi-LAT data. A temporal analysis of the gamma-ray flux during this period finds evidence of a shortest variability timescale of $\tau_{obs}$ = 6.2 $\pm$ 0.9 hours, indicating emission from compact regions within the jet, and the combined gamma-ray spectrum shows no strong evidence of a spectral cut-off. An investigation into correlations between the multiwavelength observations found evidence of optical and gamma-ray correlations, suggesting a single-zone model of emission. Finally, the multiwavelength spectral energy distribution is well described by a simple one-zone leptonic synchrotron self-Compton radiation model.
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