Implications of photon-ALP oscillations in the extragalactic neutrino source TXS 0506 +056 at sub-PeV energies

Photon-axion-like particle (ALP) oscillations result in the survival of gamma rays from distant sources above TeV energies. Studies of events observed by CAST, Fermi-LAT, and IACT have constrained the ALP parameters. We investigate the effect of photon-ALP oscillations on the gamma-ray spectra of the first extragalactic neutrino source, TXS 0506 +056 , for observations by Fermi-LAT and MAGIC around the IC170922-A alert. We obtain a constraint on the ALP coupling parameter g_{a γ}<5 ×10^-11 GeV^-1 with 95% C.L. when focusing on the ALP mass range 0.1 neV ≤m_a≤1000 neV . Importantly, we study the implications of ALP -γ oscillations on the counterpart γ rays of the sub-PeV neutrinos observed from TXS 0506 +056 . We also show the diffuse γ -ray fluxes and observabilities from flat-spectrum radio quasars, high-synchrotron peaked sources, and low-intermediate-synchrotron peaked sources, assuming similar gamma-ray emissions as that from TXS 0506 +056 .