Detection of X-ray polarized emission and accretion-disk winds with IXPE and NICER in the black-hole X-ray binary 4U 1630-47

Abstract

We detect a high level of polarization in the X-ray emission of the black-hole binary 4U 1630-47 in an observation with the Imaging X-ray Polarimetry Explorer. The 2-8 keV polarization degree is 8 % at a position angle of $18^{\circ }$, with the polarization degree increasing significantly with energy, from ~6 % at ~2 keV to ~ 11 % at ~8 keV. The continuum emission in the spectrum of simultaneous observations with the Neutron Star Interior Composition Explorer, NICER, is well described with only a thermal disc spectrum, with stringent upper limits to any Comptonized emission from the corona. Together with the lack of significant variability in the Fourier power spectrum, this suggests that the source was in the high-soft state at the time of these observations. The NICER spectrum reveals the presence of several absorption lines in the 6-9 keV band that we fit with two ionized absorbers, providing evidence of the presence of a strong disk wind, which supports the idea that the source was in the soft state. Previous measurements of X-ray polarization in other sources in harder states were associated with the corona or the jet in those systems. Given that the corona is significantly absent in this observation of 4U 1630-47, and that the jet in black-hole binaries is quenched in the high-soft state, we speculate that in this observation of 4U 1630-47, the polarization likely arises from the direct and reflected radiation of the accretion disk in this source.

9 pages, 4 figures, 3 Tables, Accepted for publication in ApJL

References in corpus (11)

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• ixpeobssim: a Simulation and Analysis Framework for the Imaging X-ray Polarimetry Explorer
• Analyzing the Data from X-ray Polarimeters with Stokes Parameters
• Design, Construction, and Test of the Gas Pixel Detectors for the IXPE Mission
• Polarized X-rays from windy accretion in Cygnus X-1
• Black hole mass determination in the X-ray binary 4U 1630--47: Scaling of spectral and variability characteristics
• Accretion geometry of the neutron star low mass X-ray binary Cyg X-2 from X-ray polarization measurements
• Accretion geometry of the black-hole binary Cygnus X-1 from X-ray polarimetry
• The comptonizing medium of the black-hole X-ray binary MAXI~J1535$-$571 through type-C quasi-periodic oscillations
• The spins of the Galactic black holes in MAXI J1535-571 and 4U 1630-472 from Insight-HXMT
• Disc and wind in black hole X-ray binary MAXIJ1820+070 observed through polarized light during its 2018 outburst

Cited by in corpus (6)

• 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 $\text{NICER}$
• X-ray Polarization of Inverse Compton Scattering by Thermal and Nonthermal Electrons