Constraining the Anisotropy of the Galactic Halo with Fast Radio Burst Dispersion Measures: A Two-point Correlation Analysis

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Abstract We propose a novel method based on the two-point cross-correlation of Fast Radio Burst (FRB) dispersion measures (DMs) to probe potential anisotropy in the Galactic halo. By utilizing five distinct halo models, i.e., modified Navarro–Frenk–White model, the spherical plus disk two-component model, triaxial prolate model (vertical), triaxial oblate model (horizontal), and pear-shaped model, we conduct a comprehensive simulation to generate two-point correlation function (2PCF) templates for each configuration. Using a selected sample of low DM FRBs from the CHIME/FRB Catalog 2, we compute observational 2PCFs by binning in Galactic latitude (Δ b = 10 ∘ ) and averaging over Galactic longitude. Through likelihood analysis based on χ 2 minimization and inner product similarity, we quantify the compatibility of each model with the observed data. Our results show that the current data cannot significantly distinguish between spherical and anisotropic models, though there is a weak statistical preference for the pear-shaped model. Nevertheless, this method demonstrates strong potential for providing meaningful constraints with more precise future observations.

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