New Bounds on Axion-Like Particles From the Fermi Large Area Telescope observation of PKS $2155-304$

TL;DR

This study uses 8.6 years of Fermi-LAT gamma-ray data to search for spectral irregularities caused by axion-like particles (ALPs) in PKS 2155-304, setting new bounds on ALP properties.

Contribution

It provides new constraints on ALP-photon coupling by analyzing gamma-ray spectra and highlights the dependence on the magnetic field of the host galaxy cluster.

Findings

No significant ALP-photon oscillation evidence found.

Constraints on ALP parameters depend on the magnetic field assumptions.

High magnetic fields (~10 μG) can exclude previously allowed ALP regions.

Abstract

The axion-like particle (ALP)-photon mixing in the magnetic field around $\gamma$-ray sources or along the line-of-sight could induce oscillation between photons and ALPs, which then causes irregularities in the $\gamma$-ray spectra. In this work we try to search for such spectral irregularities in the spectrum of PKS $2155-304$ using 8.6 years of the Fermi Large Area Telescope (Fermi-LAT) data. No significant evidence for the presence of ALP-photon oscillation is obtained, and the parameter space of ALPs is constrained. The exclusion region sensitively depends on the poorly known magnetic field of host galaxy cluster of PKS $2155-304$. If the magnetic field is as high as $\sim 10~{\rm \mu G}$, the "hole"-like parameter region allowed in Ref.~\cite{Fermi} can be ruled out.