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

Abstract

Axion-like-particles (ALPs) are one promising type of dark matter candidate particles that may generate detectable effects on \(\gamma\)-ray spectra other than the canonical weakly interacting massive particles. In this work we search for such oscillation effects in the spectra of supernova remnants caused by the photon-ALP conversion, using the Fermi Large Area Telescope data. Three bright supernova remnants, IC443, W44, and W51C, are analyzed. The inclusion of photon-ALP oscillations yields an improved fit to the \(\gamma\)-ray spectrum of IC443, which gives a statistical significance of \(4.2\sigma\) in favor of such spectral 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 (\(g_{a\gamma}< 6.6 \times 10^{-11}\,{\rm GeV}^{-1}\)) set by the CAST experiment. The systematic uncertainties of the flux measurements are found to be difficult to explain the results. We speculate that the "irregularity" displayed in the spectrum of IC443 may be due to the superposition of the emission from different parts of the remnant.