THE DISK WIND IN THE RAPIDLY SPINNING STELLAR-MASS BLACK HOLE 4U 1630–472 OBSERVED WITH NuSTAR

Abstract

We present an analysis of a short NuSTAR observation of the stellar-mass black hole and low-mass X-ray binary 4U 1630$-$472. Reflection from the inner accretion disk is clearly detected for the first time in this source, owing to the sensitivity of NuSTAR. With fits to the reflection spectrum, we find evidence for a rapidly spinning black hole, $a_{*}=0.985^{+0.005}_{-0.014}$ ($1\sigma$ statistical errors). However, archival data show that the source has relatively low radio luminosity. Recently claimed relationships between jet power and black hole spin would predict either a lower spin or a higher peak radio luminosity. We also report the clear detection of an absorption feature at $7.03\pm0.03$ keV, likely signaling a disk wind. If this line arises in dense, moderately ionized gas ($\log\xi=3.6^{+0.2}_{-0.3}$) and is dominated by He-like Fe XXV, the wind has a velocity of $v/c=0.043^{+0.002}_{-0.007}$ (12900$^{+600}_{-2100}$ km s$^{-1}$). If the line is instead associated with a more highly ionized gas ($\log\xi=6.1^{+0.7}_{-0.6}$), and is dominated by Fe XXVI, evidence of a blue-shift is only marginal, after taking systematic errors into account. Our analysis suggests the ionized wind may be launched within 200$-$1100 Rg, and may be magnetically driven.