Probing the Innermost Accretion Flow Through X-Ray Polarization

X-ray polarization offers a powerful diagnostic of the geometry and relativistic effects in black hole accretion disks. In this work, we present new simulations of polarized reflection that include the contribution of returning radiation photons bent by strong gravity back onto the disk before reaching the observer. Using a relativistic ray-tracing framework, we compute the polarization degree and angle across energy and inclination, demonstrating that returning radiation can significantly enhance polarization at high energies and modify the characteristic rotation of the polarization angle. These predictions provide key insights for interpreting current and future observations, particularly with IXPE, and highlight the importance of accurate radiative-transfer modeling in the strong-gravity regime.