VERITAS Discovery of Very High Energy Gamma-Ray Emission from S3 1227+25 and Multiwavelength Observations

A. Acharyya, C. B. Adams, A. Archer, P. Bangale, W. Benbow, A. Brill, J. L. Christiansen, A. J. Chromey, M. Errando, A. Falcone, Q. Feng, J. P. Finley, G. M. Foote, L. Fortson, A. Furniss, G. Gallagher, W. Hanlon, D. Hanna, O. Hervet, C. E. HinrichsJ. Hoang, J. Holder, W. Jin, M. N. Johnson, P. Kaaret, M. Kertzman, D. Kieda, T. K. Kleiner, N. Korzoun, F. Krennrich, M. J. Lang, M. Lundy, G. Maier, C. E. McGrath, M. J. Millard, J. Millis, C. L. Mooney, P. Moriarty, R. Mukherjee, S. O'Brien, R. A. Ong, M. Pohl, E. Pueschel, J. Quinn, K. Ragan, P. T. Reynolds, D. Ribeiro, E. Roache, I. Sadeh, A. C. Sadun, L. Saha, M. Santander, G. H. Sembroski, R. Shang, M. Splettstoesser, A. K. Talluri, J. V. Tucci, V. V. Vassiliev, D. A. Williams, S. L. Wong, Talvikki Hovatta, Svetlana G. Jorstad, Sebastian Kiehlmann, Anne Lähteenmäki, Ioannis Liodakis, Alan P. Marscher, Walter Max-Moerbeck, Anthony C.S. Readhead, Rodrigo Reeves, Paul S. Smith, Merja Tornikoski

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    3 Scopus citations

    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 2015 May 15 with the Fermi-Large Area Telescope (LAT). A combined 5 hr VERITAS exposure on May 16 and 18 resulted in a strong 13? detection with a differential photon spectral index, "= 3.8 ± 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 ? obs = 6.2 ± 0.9 hr, indicating emission from compact regions within the jet, and the combined gamma-ray spectrum shows no strong evidence of a spectral cutoff. 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.

    Original languageEnglish (US)
    Article number152
    JournalAstrophysical Journal
    Volume950
    Issue number2
    DOIs
    StatePublished - Jun 1 2023

    Bibliographical note

    Publisher Copyright:
    © 2023. The Author(s). Published by the American Astronomical Society.

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