Highly Significant Detection of X-Ray Polarization in Sco X-1 and Its Polarization Angle Misaligned With the Direction of the Radio Jet

The Imaging X-ray Polarimetry Explorer has successfully measured the X-ray polarization of Scorpius X-1, the brightest Z-source, in the 2–8 keV energy band. The degree of polarization was found to be $\sim 1.0\%$ with a polarization angle of $\sim 8$°. This measurement was conducted simultaneously with NICER, NuSTAR, and Insight-HXMT observations, enabling a detailed analysis of the source's broad-band spectrum across soft and hard X-rays. The source was observed for the majority of the time in its soft state, with occasional flaring. Furthermore, low-frequency quasiperiodic oscillations were observed. Through a spectro-polarimetric analysis, we determined that the accretion disk exhibits a polarization <3.2% (90% CL) and the Comptonized component at higher energy a polarization of $\sim 1.3\%$. An attempt was also performed to measure the polarization of the reflection component. Moreover, a rotation in X-ray polarization is observed compared to previous observations by OSO-8 and PolarLight, as well as with respect to the position angle of the radio jet. This finding suggests that the polarization may vary with the state of the source, which means a change in the geometry of the corona with the accretion flow or potentially indicating a relativistic precession.