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We probe the spectropolarimetric properties of the black-hole binary source4U 1630$-$47 in the steep power law state. We detect a significant polarizationfraction of $\sim$7 % at a polarization angle of $\sim$21 $^\circ$. The $2-12$keV NICER spectrum can be fitted with a combination of a thermal and aComptonization component, the latter characterized by a spectral index, $\Gamma\sim$2.1, along with a reflection feature at $\sim$7.0 keV. In the $2-8$ keVband, the degree of polarization of 4U 1630$-$47 in the steep power law stateis 4.4 $\sigma$ different from the value previously measured in the high softstate. In the steep power law state, the polarization fraction increases as afunction of energy but exhibits an overall drop in each energy band compared tothat of the high soft state. We propose that the decrease in the polarizationfraction in the steep power law state could be attributed to the presence of acorona. The observed polarization properties in both states can be explained bythe self-irradiation of the disk around a Kerr black hole, likely influenced bythe frame-dragging effect.

Spectropolarimetric study of 4U 1630$-$47 in Steep Power law state with IXPE and NICER