Spectral modulation of non-Galactic plane Gamma-ray pulsars due to photon-ALPs mixing in Galactic magnetic field

TL;DR

This study investigates spectral modulations in non-Galactic plane gamma-ray pulsars caused by photon-ALPs mixing in the Galactic magnetic field, providing evidence consistent with previous findings and implications for future experiments.

Contribution

It presents the first analysis of non-Galactic plane pulsar spectra for photon-ALPs mixing signatures, expanding the search beyond Galactic plane sources.

Findings

Spectral modulation detected at 3.66 sigma significance.

Results depend on the Galactic magnetic field model used.

Findings are compatible with previous Galactic plane analyses.

Abstract

In many approaches to describe physics beyond the standard model, light Nambu-Goldstone bosons (named axion-like particles or ALPS for their similarity with the axion) are predicted to exist. For ALPs with a mass of neV, photon-ALPs oscillation takes place in extra-galactic magnetic fields during the propagation of very high energy gamma-ray photons leading to excess radiation observed for optically thick sources. In order to verify this effect, gamma-ray spectra from strong Galactic plane or non-galactic plane sources can be used and the photon-ALPs mixing would lead to an energy dependent suppression of the observed gamma-ray spectra. Here, we have used Fermi-LAT observations of a sample of non Galactic plane gamma-ray pulsars located at different line-of-sights to search for spectral signatures and compare the result with the predictions using particular models for the Galactic magnetic field.We find consistent evidence with our prevoius analysis of objects located in the Galactic plane for a modulation of the spectra investigated at the level of 3.66 standard deviations . In the framework of ALPS-photon oscillation, the resulting parameters strongly depend upon the chosen magnetic field model, but seem to be within reach of new experiments(e.g. IAXO).