Document Type
Article
Publication Date
11-24-2025
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 Oð10 μGÞ 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.
Recommended Citation
Adams, C. B., Archer, A., Bangale, P., Bartkoske, J. T., Benbow, W., Chen, Y., Christiansen, J. L., Chromey, A. J., Duerr, A., Errando, M., Escobar Godoy, M., Escudero Pedrosa, J., Feldman, S., Feng, Q., Filbert, S., Fortson, L., Furniss, A., Hanlon, W., … Hervet, O. (2025). Constraints on axionlike particles from VERITAS observations of a flaring radio galaxy in the Perseus cluster. Physical Review D, 112(10). https://doi.org/10.1103/jydc-npy6
Comments
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.