A Comprehensive Chandra Study of the Disk Wind in the Black Hole Candidate 4U 1630-472

TL;DR

This study analyzes the disk wind in the black hole candidate 4U 1630-472 using Chandra observations, revealing a complex, multi-zone wind structure with evidence for magnetic driving at small radii and thermally driven components at larger scales.

Contribution

It provides the first detailed multi-zone spectral analysis of the disk wind in 4U 1630-472, highlighting the role of magnetic forces in wind launching.

Findings

Inner wind components are highly ionized with small radii and likely magnetically driven.

Outer wind components are less ionized, larger in radius, and consistent with thermal driving.

The wind structure suggests a magneto-thermal hybrid origin.

Abstract

The mechanisms that drive disk winds are a window into the physical processes that underlie the disk. Stellar-mass black holes are an ideal setting in which to explore these mechanisms, in part because their outbursts span a broad range in mass accretion rate. We performed a spectral analysis of the disk wind found in six Chandra/HETG observations of the black hole candidate 4U~1630$-$472, covering a range of luminosities over two distinct spectral states. We modeled both wind absorption and extended wind re-emission components using PION, a self-consistent photoionized absorption model. In all but one case, two photoionization zones were required in order to obtain acceptable fits. Two independent constraints on launching radii, obtained via the ionization parameter formalism and the dynamical broadening of the re-emission, helped characterize the geometry of the wind. The innermost wind components ($r \simeq {10}^{2-3}$ $GM/{c}^{2}$) tend towards small volume filling factors, high ionization, densities up to $n \simeq {10}^{15-16} {\text{cm}}^{-3}$, and outflow velocities of $\sim 0.003c$. These small launching radii and large densities require magnetic driving, as they are inconsistent with numerical and analytical treatments of thermally driven winds. Outer wind components ($r \simeq {10}^{5}$ $GM/{c}^{2}$) are significantly less ionized and have filling factors near unity. Their larger launching radii, lower densities ($n \simeq {10}^{12} {\text{cm}}^{-3}$), and outflow velocities ($\sim 0.0007c$) are nominally consistent with thermally driven winds. The overall wind structure suggests that these components may also be part of a broader MHD outflow and perhaps better described as magneto-thermal hybrid winds.