Photon-ALP beam propagation from Mrk 501

Very-high-energy ($E>100\text{ }\text{ }\mathrm{GeV}$) $\ensuremath{\gamma}$-ray observations offer the possibility of indirectly detecting the presence of axion-like particles (ALPs). This paper focuses on detecting photon-ALP oscillations in $\ensuremath{\gamma}$-ray spectra from distant sources in astrophysical magnetic fields. Strong evidence indicates that 1) photon-ALP oscillations can effectively decrease photon absorption at energies of several tens of TeV---caused by the extragalactic background light---to a level able to better explain the observational data, and 2) the impact of magnetic-field models in photon-ALP beams crossing several magnetized media is significant. We revisit the expected signature for the photon-ALP oscillation effects on $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ absorption in the TeV spectra of Mrk 501. The result is that the photon-ALP beam propagation with mass ${m}_{a}\ensuremath{\sim}{10}^{\ensuremath{-}10}\text{ }\text{ }\mathrm{eV}$ and two-photon coupling constant ${g}_{a\ensuremath{\gamma}}\ensuremath{\sim}0.417\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}11}\text{ }\text{ }{\mathrm{GeV}}^{\ensuremath{-}1}$ crossing reasonable magnetic field scenarios considered here can roughly reproduce the observed TeV $\ensuremath{\gamma}$-ray spectra for Mrk 501.