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

Abstract

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 disk dominated thermal state (kT${}_{in}\approx 1.4$ keV) with clear detection of absorption features at $6.69\pm 0.01$ keV and $6.97\pm 0.01$ keV from both NICER as well as IXPE spectra, likely indicating a coupling of disk-wind. A significant degree of polarization(PD) $=8.33\pm 0.17\%$ and polarization angle(PA) $=17.78^{\circ }\pm 0.60^{\circ }$ in the energy range of $2-8$ keV 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 $0.5-12$ keV are modelled to study the spectral properties. Furthermore, the spin parameter of the black hole is estimated with spectro-polarimetric data as a${}_{\ast }=0.927\pm 0.001(1\sigma )$ which is corroborated by NICER observations. Finally, we discuss the implications of our findings.

6 pages, 4 figures, 4 tables, Accepted for publication in MNRAS Letters

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• X-ray Polarization of the Black Hole X-ray Binary 4U 1630-47 Challenges Standard Thin Accretion Disk Scenario
• X-ray polarisation properties of thermal-radiative disc winds in binary systems
• Spectral and polarization properties of reflected X-ray emission from black-hole accretion discs for a distant observer: the lamp-post model
• Spectropolarimetric study of 4U 1630$-$47 in Steep Power law state with IXPE and NICER
• Spectro-temporal Investigation of Quasi-periodic Oscillations From Black Hole X-ray Binary 4U 1630-472 Using $\text{NICER}$
• Accretion Geometry of Black Hole X-ray Binaries: Insights from X-ray Observations
• NICER Spectral and Timing Analysis of 4U 1630$-$47 and its Heartbeat State
• X-ray Polarization of Inverse Compton Scattering by Thermal and Nonthermal Electrons