Dipanjan Banerjee

We present a broadband spectropolarimetric analysis of the extragalactic radio source RACS_0900-28_7036 using Spectra and Polarization in Cutouts of Extragalactic Sources (SPICE-RACS) DR2 observations with the Australian Square Kilometre Array Pathfinder (ASKAP). The source was selected for its large rotation measure (RM = 345.7 ± 0.2 rad m ⁻² ), substantial excess relative to the local foreground (ΔRM ≈ 171 rad m ⁻² ), and strong evidence of Faraday complexity ( σ _add / δσ _add ≈ 8.6). Observations span 803–1083 MHz in 36 spectral channels, enabling detailed characterization of Faraday rotation and wavelength-dependent depolarization. One-dimensional QU fitting and Bayesian model selection identify a multicomponent model comprising one Burn-slab component and two external Faraday dispersion (EFD) components (1 Slab + 2 EFDs) as the preferred description. The dominant astrophysical component exhibits RM ≈ 345.5 rad m ⁻² with modest Faraday dispersion ( σ _RM ≈ 3 rad m ⁻² ), consistent with the Galactic foreground RM at the source position (RM _Gal = 331.9 ± 33.1 rad m ⁻² ). A secondary broader component at RM ≈ 131.5 rad m ⁻² shows strong depolarization ( σ _RM ≈ 19.5 rad m ⁻² ), indicating an additional turbulent Faraday-active medium along the line of sight. The fractional polarization spectrum and q – u plane evolution further confirm multiple Faraday-active regions along the line of sight. These results demonstrate that ASKAP broadband spectropolarimetry can resolve complex Faraday structures and probe turbulent magnetized environments, providing a framework for systematic depolarization studies across the full SPICE-RACS catalog and enabling statistical investigations of Faraday complexity in diverse extragalactic radio sources.