X-ray polarimetric features of Gamma-ray Bursts across varied redshifts and hints for Axion-Like-Particles

Abstract

Polarimetric features during the prompt phase of Gamma-ray Bursts (GRBs) have been essential for elucidating the debated emission mechanisms and gaining insight into the inner structure of GRBs. However, the potential impact of photon-Axion-Like-Particle (ALP) mixing in extragalactic magnetic fields, leading to significant modifications to the initial polarization state, has been overlooked in discussions concerning prompt phase constraints. In this work, we first examine the statistical characteristics of linear polarization degree ($\Pi_{L}$) in GRBs, by utilizing data from polarimetric missions focusing on sub-MeV emissions. Our analysis, conducted with a restricted sample of GRBs spanning various redshifts, reveals a diverse distribution of $\Pi_{L}$, which currently shows no correlation with the GRBs' spectral parameters or properties of candidate host galaxies. We then explore alternations to the initial $\Pi_{L}$ due to photon-ALP mixing within a domain-like structure of the intergalactic magnetic field (${\bf B}_{\rm IGM} $). With the existence of ALPs with $m_{a}$$~$$\lesssim$$~$$10^{-14}$$~$eV and $g_{a\gamma}~$$\simeq$$~0.5\times10^{-11}$, the mixing leads to a decrease in the polarization degree of initially fully linearly polarized photons, while it induces a certain degree of polarization to initially unpolarized photons. To ensure that the effect of mixing is small enough to be negligible, the mixing term $\Delta_{a\gamma} \equiv 1/2\ g_{a\gamma} {\bf B}_{\rm IGM}$ should be less than $1.5\times 10^{-4}$ Mpc$^{-1}$. Currently, the number of GRBs with both sub-MeV polarization measurement and redshift confirmation remains very limited. Certification of redshift for GRBs with low $\Pi_{L}$ would further constrain the parameter space of ALPs or provide an independent means to determine the upper limit on ${\bf B}_{\rm IGM}$.