VERITAS discovery of very high energy gamma-ray emission from S3 1227+25 and multiwavelength observations
Creators: name: Acharyya, Atreya
name: Adams, Colin
name: Archer, Avery
name: Bangale, Priyadarshini
name: Benbow, Wystan
name: Brill, Aryeh
name: Christiansen, Jodi
name: Chromey, Alisha
name: Errando, Manel
name: Falcone, Abe
name: Feng, Qi
name: Finley, John
name: Foote, Gregory
name: Fortson, Lucy
name: Furniss, Amy
name: Gallagher, Greg
name: Hanlon, William
name: Hanna, David
name: Hervet, Olivier
name: Hinrichs, Claire
name: Hoang, John
name: Holder, Jamie
name: Jin, Weidong
name: Johnson, Madalyn
name: Kaaret, Philip
name: Kertzman, Mary P.
name: Kieda, David
name: Kleiner, Tobias
name: Korzoun, Nikolas
name: Krennrich, Frank
name: Lang, Mark
name: Lundy, Matthew
name: Maier, Gernot
name: McGrath, Conor
name: Millard, Matthew
name: Millis, John
name: Mooney, Connor
name: Moriarty, Patrick
name: Mukherjee, Reshmi
name: O'Brien, Stephan
name: Ong, Rene A.
name: Pohl, Martin
name: Pueschel, Elisa
name: Quinn, John
name: Ragan, Kenneth J.
name: Reynolds, Paul
name: Ribeiro, Deivid
name: Roache, Emmet Thomas
name: Sadeh, Iftach
name: Sadun, Alberto
name: Saha, Lab
name: Santander, Marcos
name: Sembroski, Glenn
name: Shang, Ruo
name: Splettstoesser, Megan
name: Talluri, Anjana
name: Tucci, James
name: Vassiliev, Vladimir
name: Williams, David
name: Wong, Sam
name: Hovatta, Talvikki
name: Jorstad, Svetlana
name: Kiehlmann, Sebastian
name: Lahteenmaki, Anne
name: Liodakis, Ioannis
name: Marscher, Alan
name: Max-Moerbeck, Walter
name: Readhead, Anthony
name: Reeves, Rodrigo
name: Smith, Paul S
name: Tornikoski, Merja
Publisher: name: arXiv
Year: 2023
Subjects: subject: High Energy Astrophysical Phenomena (astro-ph.HE)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: 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$σ$ detection with a differential photon spectral index, $Γ$ = 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 $τ_{obs}$ = 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.
description: 18 pages, 6 figures. Accepted for publication in the Astrophysical Journal (ApJ)