Soft Spectro-polarimetry of X-ray Binaries LMC X-3 and Her X-1: IXPE Insights

Spectro-temporal analysis of X-ray binaries have provided insights into their accretion geometry, yet uncertainties persist regarding the nature of the cold accretion disc and hot coronal components of the accretion flow. X-ray polarization provides an additional tool to resolve the ambiguities in accretion models. We perform a spectro-polarimetric study of the X-ray pulsar Her X-1 and a black hole X-ray binary LMC X-3 using IXPE, NICER, and Swift/XRT observations. Our findings reveal a significant 9% change in polarization degree (PD) between high and low flux states of superorbital period for Her X-1, suggesting preferential obstruction of a magnetic pole by the tilted accretion disc. In LMC X-3, we found a PD of ~3% at a polarisation angle (PA) of ~135 deg in 2-8 keV band. We also find that PD increases by 5% with PA remaining constant within 2-8 keV, indicating a static coronal slab geometry. We emphasize the significance of our conclusions.