X-ray Polarization of the Black Hole X-ray Binary 4U 1630-47 Challenges Standard Thin Accretion Disk Scenario

Abstract

Large energy-dependent X-ray polarization degree is detected by the Imaging X-ray Polarimetry Explorer ({IXPE}) in the high-soft emission state of the black hole X-ray binary 4U 1630--47. The highly significant detection (at $\approx 50\sigma$ confidence level) of an unexpectedly high polarization, rising from $\sim 6\%$ at $2$ keV to $\sim 10\%$ at $8$ keV, cannot be easily reconciled with standard models of thin accretion discs. In this work we compare the predictions of different theoretical models with the {IXPE} data and conclude that the observed polarization properties are compatible with a scenario in which matter accretes onto the black hole through a thin disc, covered by a partially-ionized atmosphere flowing away at mildly relativistic velocities.

Published in ApJ (https://doi.org/10.3847/1538-4357/ad226e)

References in corpus (22)

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Cited by in corpus (10)

• Dramatic Drop in the X-Ray Polarization of Swift J1727.8$-$1613 in the Soft Spectral State
• X-ray polarization from accretion disk winds
• Relativistic reflection within an extended hot plasma geometry
• 20 years of disk winds in 4U 1630-47 -- I. Long-term behavior and influence of hard X-rays
• Possible Coronal Geometry in the Hard and Soft State of Black Hole X-ray Binaries from MONK Simulations
• X-ray linear polarization prediction in Black-Hole binaries and Active Galactic Nuclei and its measurements by IXPE
• Accretion Geometry of Black Hole X-ray Binaries: Insights from X-ray Observations
• The peculiar disk evolution of 4U 1630--472 observed by Insight-HXMT during the 2022 and 2023 outbursts
• NICER Spectral and Timing Analysis of 4U 1630$-$47 and its Heartbeat State
• X-ray Polarization of Inverse Compton Scattering by Thermal and Nonthermal Electrons