Limits on axionlike particles from Mrk 421 with 4.5-year period observations by ARGO-YBJ and Fermi-LAT

In this work, we investigate the axionlike particle (ALP)-photon oscillation effect in the spectra of the blazar Markarian 421 (Mrk 421) using 4.5 years of the Astrophysical Radiation with Ground-based Observatory at YangBaJing (ARGO-YBJ) and Fermi Large Area Telescope (Fermi-LAT) data. These data are collected during the common operation time, which cover ten activity phases of Mrk 421. No significant ALP-photon oscillation effect is confirmed. On the other hand, not all the observations of the ten phases can be individually used to set the 95% confidence level (C.L.) constraint on the ALP parameter space. However, the constraint can be significantly improved if the analyses for the ten phases are combined. We find that the upper limit at 95% C.L. on the ALP-photon coupling g_{a γ} set by the ARGO-YBJ and Fermi-LAT observations of Mrk 421 is within ∼[2 ×10^-11,6 ×10^-11] GeV^-1 for the ALP mass of ∼5 ×10^-10 eV ≲m_a≲5 ×10^-7 eV .