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Constraints on axionlike particles from VERITAS observations of a flaring radio galaxy in the Perseus cluster

C. B. Adams1,*, A. Archer2, P. Bangale3, J. T. Bartkoske4, W. Benbow5, Y. Chen6, J. L. Christiansen7, A. J. Chromey5, A. Duerr4 et al. (VERITAS Collaboration)

A. Duerr4, M. Errando8, M. Escobar Godoy9, J. Escudero Pedrosa10, S. Feldman6, Q. Feng4,†, S. Filbert4, L. Fortson11, A. Furniss9, W. Hanlon5, O. Hervet9, C. E. Hinrichs12, J. Holder3, Z. Hughes8, T. B. Humensky13, M. Iskakova8, W. Jin6, P. Kaaret14, M. Kertzman2, M. Kherlakian15, D. Kieda4, T. K. Kleiner16, N. Korzoun3, F. Krennrich17, S. Kumar18, S. Kundu19, M. J. Lang20, M. Lundy21, P. Moriarty20, R. Mukherjee22, W. Ning6, R. A. Ong6, A. Pandey4, M. Pohl23, E. Pueschel15, J. Quinn24, P. L. Rabinowitz8, K. Ragan21, P. T. Reynolds25, D. Ribeiro11, E. Roache5, C. Rulten11,26, I. Sadeh16, L. Saha5, M. Santander19, G. H. Sembroski27, R. Shang22, D. Tak28, A. K. Talluri11, J. V. Tucci29, J. Valverde30, V. V. Vassiliev6, D. A. Williams9, S. L. Wong21, J. Woo31, T. Yoshikoshi32, and M. Meyer33 (VERITAS Collaboration)

  • 1Physics Department, Columbia University, New York, New York 10027, USA
  • 2Department of Physics and Astronomy, DePauw University, Greencastle, Indiana 46135-0037, USA
  • 3Department of Physics and Astronomy and the Bartol Research Institute, University of Delaware, Newark, Delaware 19716, USA
  • 4Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112, USA
  • 5Center for Astrophysics | Harvard & Smithsonian, Cambridge, Massachusetts 02138, USA
  • 6Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
  • 7Physics Department, California Polytechnic State University, San Luis Obispo, California 94307, USA
  • 8Department of Physics, Washington University, St. Louis, Missouri 63130, USA
  • 9Santa Cruz Institute for Particle Physics and Department of Physics, University of California, Santa Cruz, California 95064, USA
  • 10Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, USA
  • 11School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA
  • 12Center for Astrophysics | Harvard & Smithsonian, Cambridge, Massachusetts 02138, USA and Department of Physics and Astronomy, Dartmouth College, 6127 Wilder Laboratory, Hanover, New Hampshire 03755, USA
  • 13Department of Physics, University of Maryland, College Park, Maryland, USA and NASA GSFC, Greenbelt, Maryland 20771, USA
  • 14Department of Physics and Astronomy, University of Iowa, Van Allen Hall, Iowa City, Iowa 52242, USA
  • 15Fakultät für Physik & Astronomie, Ruhr-Universität Bochum, D-44780 Bochum, Germany
  • 16DESY, Platanenallee 6, 15738 Zeuthen, Germany
  • 17Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA
  • 18Department of Physics, University of Maryland, College Park, Maryland, USA
  • 19Department of Physics and Astronomy, University of Alabama, Tuscaloosa, Alabama 35487, USA
  • 20School of Natural Sciences, University of Galway, University Road, Galway, H91 TK33, Ireland
  • 21Physics Department, McGill University, Montreal, Quebec H3A 2T8, Canada
  • 22Department of Physics and Astronomy, Barnard College, Columbia University, New York 10027, USA
  • 23Institute of Physics and Astronomy, University of Potsdam, 14476 Potsdam-Golm, Germany and DESY, Platanenallee 6, 15738 Zeuthen, Germany
  • 24School of Physics, University College Dublin, Belfield, Dublin 4, Ireland
  • 25Department of Physical Sciences, Munster Technological University, Bishopstown, Cork T12 P928, Ireland
  • 26Centre for Advanced Instrumentation, Department of Physics, University of Durham, South Road, Durham DH1 3LE, United Kingdom
  • 27Department of Physics and Astronomy, Purdue University, West Lafayette, Indiana 47907, USA
  • 28SNU Astronomy Research Center, Seoul National University, Seoul 08826, Republic of Korea
  • 29Department of Physics, Indiana University Indianapolis, Indianapolis, Indiana 46202, USA
  • 30Department of Physics, University of Maryland, Baltimore County, Baltimore Maryland 21250, USA and NASA GSFC, Greenbelt, Maryland 20771, USA
  • 31Columbia Astrophysics Laboratory, Columbia University, New York, New York 10027, USA
  • 32Institute for Cosmic Ray Research, University of Tokyo, 5-1-5, Kashiwa-no-ha, Kashiwa, Chiba 277-8582, Japan
  • 33CP3-Origins, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark

  • *Contact author: ca2762@columbia.edu
  • †Contact author: qi.feng@utah.edu
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Phys. Rev. D 112, 103044 – Published 24 November, 2025

DOI: https://doi.org/10.1103/jydc-npy6

Abstract

Axion-like particles (ALPs) are hypothetical particles that emerge in numerous theoretical extensions to the Standard Model. Their coupling to electromagnetic field implies that ALPs would mix with photons in the presence of external magnetic fields. As ALP phenomenology is governed by the mass and strength of its coupling, there is a subset of this parameter space in which this mixing would be expected to leave an imprint on the spectra of TeV γ-ray sources. In 2017, the VERITAS γ-ray observatory recorded the second day of a dramatic flare of the radio galaxy NGC 1275, embedded at the center of the Perseus galaxy cluster. This serendipitous locale provides a spatially-extended magnetic field of strength O(10  μG) through which escaping photons traverse, making it an excellent target to study ALPs. We analyze the VERITAS data of NGC 1275’s 2017 flare with the gammapy analysis package. Extensive fitting and modeling are performed to ultimately conduct a likelihood analysis used to search for any evidence of a preference for ALPs and to explore the confidence with which constraints can be set. We adopt the CLs method for this study for its conservative approach to setting limits in regimes where the search has limited sensitivity. No evidence for the existence of ALPs is found, and no combination of mass and coupling strength can be excluded at or above 95% confidence level. We provide a map showing the strength of our exclusions in the mass and coupling parameter space. The strongest exclusions are found in the mass range 2×10−7  eV≲ma≲4×10−7  eV and at the coupling strength of gaγ≳3×10−11  GeV−1 up to 80% confidence level, which are consistent with previous studies. We find the CLs to be a trustworthy approach, and advocate for its continued usage in future studies. We note that many of the limitations contributing to the limited sensitivity seen by VERITAS in this study will be improved with next-generation γ-ray instruments, such as the Cherenkov Telescope Array Observatory.

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Phys. Rev. D 112, 103044– Published 24 November, 2025
  • Received 1 August 2025
  • Accepted 20 October 2025
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