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PreprintCC BY 4.0arXiv

Multi-Period Fermi-LAT and LHAASO Constraints on Axion-Like Particles from Mrk 421 via χ2 Profile Likelihood with Gaussian Copula Correlation

  • Longhua Qin
  • Jiancheng Wang
  • Chuyuan Yang
  • Huaizhen Li
  • Ao Wang
  • Weiwei Na
  • Hushan Xu
  • Zhongtao Han
  • Xiaogu Zhong
  • Zunli Yuan
  • Yubin Li
  • Guangbo Long
Open at sourcePDFDOICite

Abstract

We present a joint multi-period analysis of axion-like particles (ALPs) using five sets of simultaneous Fermi-LAT and LHAASO observations of the TeV blazar Mrk~421. Photon-ALP oscillations are calculated self-consistently together with EBL absorption for two representative jet emission models: a two-zone hybrid model and a single-zone hadronic model. To account for weak correlations among different observational epochs, we adopt a χ2-based profile analysis combined with a Gaussian copula (ρ=0.03). Nuisance parameters are optimized under the no-ALP hypothesis before profiling the ALP parameters ma and gaγ. In the low-mass regime (ma≲1\,neV) we obtain a 95\% CL upper limit of gaγ=6.35×10−13 GeV−1. Over the full mass range $0.1−−500$\,neV, the most conservative 95\% CL upper limits are gaγ<6.69×10−12 GeV−1 (two-zone) and gaγ<7.37×10−12 GeV−1 (single-zone). Variations of the EBL template, the Galactic and intergalactic magnetic-field models, the spectral binning, and residual instrumental systematics change these limits by only a few percent. The jet magnetic field is the leading systematic and can shift the low-mass bound by a factor of a few; only a substantially weaker single-zone field degrades the constraint by about an order of magnitude. The analysis framework developed here provides a statistically consistent approach for future ALP searches with multi-messenger gamma-ray data.

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Cite

BibTeXRIS
BibTeX
@misc{qin2026multiperiod,
  title = {{Multi-Period Fermi-LAT and LHAASO Constraints on Axion-Like Particles from Mrk 421 via $χ^2$ Profile Likelihood with Gaussian Copula Correlation}},
  author = {Longhua Qin and Jiancheng Wang and Chuyuan Yang and Huaizhen Li and Ao Wang and Weiwei Na and Hushan Xu and Zhongtao Han and Xiaogu Zhong and Zunli Yuan and Yubin Li and Guangbo Long},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2606.05738},
  eprint = {2606.05738},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2606.05738},
  note = {CC BY 4.0},
}
RIS
TY  - UNPB
TI  - Multi-Period Fermi-LAT and LHAASO Constraints on Axion-Like Particles from Mrk 421 via χ^2 Profile Likelihood with Gaussian Copula Correlation
AU  - Longhua Qin
AU  - Jiancheng Wang
AU  - Chuyuan Yang
AU  - Huaizhen Li
AU  - Ao Wang
AU  - Weiwei Na
AU  - Hushan Xu
AU  - Zhongtao Han
AU  - Xiaogu Zhong
AU  - Zunli Yuan
AU  - Yubin Li
AU  - Guangbo Long
PY  - 2026
DA  - 2026/10/11
PB  - arXiv
DO  - 10.48550/arxiv.2606.05738
UR  - https://arxiv.org/abs/2606.05738
AB  - We present a joint multi-period analysis of axion-like particles (ALPs) using five sets of simultaneous Fermi-LAT and LHAASO observations of the TeV blazar Mrk~421. Photon-ALP oscillations are calculated self-consistently together with EBL absorption for two representative jet emission models: a two-zone hybrid model and a single-zone hadronic model. To account for weak correlations among different observational epochs, we adopt a χ^2-based profile analysis combined with a Gaussian copula (ρ=0.03). Nuisance parameters are optimized under the no-ALP hypothesis before profiling the ALP parameters m_a and g_aγ. In the low-mass regime (m_a≲1\,neV) we obtain a 95\% CL upper limit of g_aγ=6.35×10^−13 GeV^−1. Over the full mass range $0.1−−500$\,neV, the most conservative 95\% CL upper limits are g_aγ<6.69×10^−12 GeV^−1 (two-zone) and g_aγ<7.37×10^−12 GeV^−1 (single-zone). Variations of the EBL template, the Galactic and intergalactic magnetic-field models, the spectral binning, and residual instrumental systematics change these limits by only a few percent. The jet magnetic field is the leading systematic and can shift the low-mass bound by a factor of a few; only a substantially weaker single-zone field degrades the constraint by about an order of magnitude. The analysis framework developed here provides a statistically consistent approach for future ALP searches with multi-messenger gamma-ray data.
ER  -