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

TL;DR

This study searches for photon-axionlike particle oscillations in gamma-ray spectra of supernova remnants using Fermi-LAT data, finding a potential signal in IC443 but with parameters conflicting with existing bounds.

Contribution

It presents the first search for spectral oscillations caused by ALPs in supernova remnants using Fermi-LAT data, and reports a possible detection with tension to current experimental limits.

Findings

Improved fit to IC443 spectrum with ALP oscillation model

Potential ALP signal with 4.2σ significance in IC443

Best-fit ALP parameters conflict with CAST bounds

Abstract

Axionlike-particles (ALPs) are one promising type of dark matter candidate particle 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. It is difficult to explain the results using the systematic uncertainties of the flux measurements. 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.