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

Abstract

Axion like particles (ALPs) are fundamental pseudo scalar particles with properties similar to Axions that have been invoked to solve the strong CP problem in Quantum Chromodynamics. ALPs can oscillate into photons and vice versa in the presence of an external magnetic field. This oscillation of Photon and ALPs could have important implications for astronomical observations, i.e. a characteristic energy dependent attenuation in Gamma ray spectra for astrophysical sources. Here we have revisited the opportunity to search Photon-ALPs coupling in the disappearance channel. We use nine years of Fermi Pass 8 data of a selection of non-Galactic plane Gamma-ray source candidates and study the modulation in the spectra in accordance with Photon-ALPs mixing and estimate best fit values of the parameters i.e. Photon-ALPs coupling constant (g_αγγ ) and ALPs mass(m_α ). For the magnetic field we assume large scale galactic magnetic field models based on Faraday rotation measurements. 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).