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Axionlike-particles (ALPs) are one promising type of dark matter candidateparticle that may generate detectable effects on $\gamma$-ray spectra otherthan the canonical weakly interacting massive particles. In this work we searchfor such oscillation effects in the spectra of supernova remnants caused by thephoton-ALP conversion, using the Fermi Large Area Telescope data. Three brightsupernova remnants, IC443, W44, and W51C, are analyzed. The inclusion ofphoton-ALP oscillations yields an improved fit to the $\gamma$-ray spectrum ofIC443, which gives a statistical significance of $4.2\sigma$ in favor of suchspectral oscillation. However, the best-fit parameters of ALPs($m_{a}=6.6\,{\rm neV}$, $g_{a\gamma}=13.4 \times 10^{-11}\,{\rm GeV}^{-1}$)are in tension with the upper bound ($g_{a\gamma}< 6.6 \times 10^{-11}\,{\rmGeV}^{-1}$) set by the CAST experiment. It is difficult to explain the resultsusing the systematic uncertainties of the flux measurements. We speculate thatthe "irregularity" displayed in the spectrum of IC443 may be due to thesuperposition of the emission from different parts of the remnant.

Searching for spectral oscillations due to photon-axionlike particle conversion using the Fermi-LAT observations of bright supernova remnants