Article

The Hard State of the Highly Absorbed High Inclination Black Hole Binary Candidate Swift J1658.2–4242 Observed by NuSTAR and Swift

Y. XuCahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125, USAFiona A. HarrisonCahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125, USAJ. A. KenneaDepartment of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Lab, University Park, PA 16802, USAD. J. WaltonInstitute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UKJohn A. TomsickSpace Sciences Laboratory, 7 Gauss Way, University of California, Berkeley, CA 94720-7450, USAJon M. MillerDepartment of Astronomy, University of Michigan, 1085 South University Avenue, Ann Arbor, MI 48109, USAD. BarretCNRS, IRAP, 9 Av. colonel Roche, BP 44346, F-31028 Toulouse cedex 4, FranceA. C. FabianInstitute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UKKarl ForsterCahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125, USAF. FuerstEuropean Space Astronomy Centre (ESA/ESAC), Operations Department, Villanueva de la Cañada (Madrid), SpainP. GandhiDepartment of Physics and Astronomy, University of Southampton, SO17 3RT, UKJavier A. GarcíaCahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125, USA

2018en

ABI

Abstract

Abstract We present a spectral and timing analysis of the newly reported Galactic X-ray transient Swift J1658.2–4242 observed by Nuclear Spectroscopic Telescope Array (NuSTAR) and Swift . The broadband X-ray continuum is typical of a black hole binary in the bright hard state, with a photon index of Γ = 1.63 ± 0.02 and a low coronal temperature of kT e = 22 ± 1 keV, corresponding to a low spectral cutoff well constrained by NuSTAR . Spectral modeling of the relativistic disk reflection features, consisting of a broad Fe K α line and the Compton reflection hump, reveals that the black hole is rapidly spinning with the spin parameter of a * > 0.96, and the inner accretion disk is viewed at a high inclination angle of (statistical errors, 90% confidence). The high inclination is independently confirmed by dips in the light curves, which can be explained by absorbing material located near the disk plane temporarily obscuring the central region. In addition, we detect an absorption line in the NuSTAR spectra centered at keV. If associated with ionized Fe K absorption lines, this provides evidence for the presence of outflowing material in the low/hard state of a black hole binary candidate. A timing analysis shows the presence of a type-C quasi-periodic oscillation in the power spectrum, with the frequency increasing from ∼0.14 to ∼0.21 Hz during the single NuSTAR exposure. Our analysis reveals that Swift J1658.2–4242 displays characteristics typical for a black hole binary that is viewed at a high inclination angle, making it a good system for studying the accretion geometry in black hole binaries.

Identifiers

DOI: 10.3847/1538-4357/aada03

Citations and references

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