Probing μeV ALPs with future LHAASO observations of AGN γ-ray spectra

Guangbo Long, Siyu Chen, Shuo Xu, and Hong-Hao Zhang
Phys. Rev. D 104, 083014 – Published 7 October 2021

Abstract

Axionlike particles (ALPs) are predicted in some well-motivated theories beyond the Standard Model. The TeV gamma-rays from active galactic nuclei (AGN) suffer attenuation by the pair production interactions with the cosmic background light (EBL/CMB) during its travel to the earth. The attenuation can be circumvented through photon-ALP conversions in the AGN and Galaxy magnetic-field, and a flux enhancement is expected to arise in the observed spectrum. In this work, we study the potential of the AGN gamma-ray spectrum for energy up to above 100 TeV to probe ALP-parameter space at around μeV, where the coupling gaγ is so far relatively weakly constrained. We find the nearby and bright sources, Mrk 501, IC 310 and M 87, are suitable for our objective. Assuming an intrinsic spectrum exponential cutoff energy, we extrapolate the observed spectra of these sources up to above 100 TeV by the models with/without ALPs. For gaγ2×1011GeV1 with ma0.5μeV, the flux at around 100 TeV predicted by the ALP model can be enhanced more than an order of magnitude than that from the standard absorption, and could be detected by LHAASO. Our result is subject to the uncertainty from the intrinsic cutoff energy and the AGN lobe (or plume) magnetic-field. For an optimistic estimation, the constraint can be improved to gaγ2×1011GeV1 with ma1μeV. This require further observations on these sources by the forthcoming CTA, LHAASO, SWGO and so on.

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  • Received 29 January 2021
  • Revised 8 July 2021
  • Accepted 9 September 2021

DOI:https://doi.org/10.1103/PhysRevD.104.083014

© 2021 American Physical Society

Physics Subject Headings (PhySH)

Particles & FieldsGravitation, Cosmology & Astrophysics

Authors & Affiliations

Guangbo Long, Siyu Chen, Shuo Xu, and Hong-Hao Zhang*

  • School of Physics, Sun Yat-Sen University, Guangzhou 510275, China

  • *Corresponding author. zhh98@mail.sysu.edu.cn

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Issue

Vol. 104, Iss. 8 — 15 October 2021

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