IXPE and NICER view of black hole X-ray binary 4U 1630-47: First significant detection of polarized emission in thermal state

We present a detailed spectro-polarimetric study of black hole X-ray binary 4U 1630-47 during its 2022 outburst with IXPE and NICER observations. The source is observed in disc dominated thermal state (kT(in) approximate to 1.4keV) with clear detection of absorption features at 6.69 +/- 0.01keV and 6.97 +/- 0.01keV from both NICER as well as IXPE spectra, likely indicating a coupling of disc-wind. A significant degree of polarization (PD) and polarization angle (PA) =17.78 degrees +/- 0.60 degrees in the energy range of 2 - 8keV are measured with IXPE. PD is found to be an increasing function of energy whereas PA remains roughly same within the energy range. Simultaneous energy spectra from NICER in the range of 0.5 - 12keV are modelled to study the spectral properties. Furthermore, the spin parameter of the black hole is estimated with spectro-polarimetric data as a which is corroborated by NICER observations. Finally, we discuss the implications of our findings.