X-ray polarimetric features of gamma-ray bursts across varied redshifts and hints for axionlike 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-axionlike 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 (ΠL) 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 ΠL, which currently shows no correlation with the GRBs' spectral parameters or properties of candidate host galaxies. We then explore alternations to the initial ΠL due to photon-ALP mixing within a domainlike structure of the intergalactic magnetic field (BIGM), considering various parameter sets associated with ALPs (ma, gaγ) and BIGM. For ALPs with ma≲10-14 eV, photon-ALP mixing decreases the polarization degree of initially fully polarized photons (ΠL0=1) and induces polarization in initially unpolarized photons (ΠL0=0). Significant alterations to ΠL0 are expected when the mixing term Δaγ≡1/2gaγBIGM exceeds 1.5×10-4 Mpc-1. The primary feature of the final ΠL as a function of the source redshifts is that ΠL approaches a midrange value for a significant Δaγ achieved when photons are emitted from high-redshift GRBs, regardless of the assumed initial ΠL0. Currently, the number of GRBs with both sub-MeV polarization measurement and redshift confirmation remains very limited. Half of the GRBs with available polarization data have ΠL being less than 30%. Certification of redshift for this subset of GRBs would further constrain the parameter space of low-mass ALPs or provide an independent means to determine the upper limit on BIGM.