NuSTAR and XMM-Newton Observations of the 2015 Outburst Decay of GX 339-4

Journal Article · Thu Jul 20 04:00:00 EDT 2017 · Astrophysical Journal

DOI:https://doi.org/10.3847/1538-4357/AA774E· OSTI ID:22663389

Stiele, H.; Kong, A. K. H., ^[1]

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1. National Tsing Hua University, Department of Physics and Institute of Astronomy, No. 101 Sect. 2 Kuang-Fu Road, 30013, Hsinchu, Taiwan (China)

The extent of the accretion disk in the low/hard state of stellar mass black hole X-ray binaries remains an open question. There is some evidence suggesting that the inner accretion disk is truncated and replaced by a hot flow, while the detection of relativistic broadened iron emission lines seems to require an accretion disk extending fully to the innermost stable circular orbit. We present comprehensive spectral and timing analyses of six Nuclear Spectroscopic Telescope Array and XMM-Newton observations of GX 339–4 taken during outburst decay in the autumn of 2015. Using a spectral model consisting of a thermal accretion disk, Comptonized emission, and a relativistic reflection component, we obtain a decreasing photon index, consistent with an X-ray binary during outburst decay. Although we observe a discrepancy in the inner radius of the accretion disk and that of the reflector, which can be attributed to the different underlying assumptions in each model, both model components indicate a truncated accretion disk that resiles with decreasing luminosity. The evolution of the characteristic frequency in Fourier power spectra and their missing energy dependence support the interpretation of a truncated and evolving disk in the hard state. The XMM-Newton data set allowed us to study, for the first time, the evolution of the covariance spectra and ratio during outburst decay. The covariance ratio increases and steeps during outburst decay, consistent with increased disk instabilities.

• OSTI ID: 22663389
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 844; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ACCRETION DISKS
BINARY STARS
BLACK HOLES
COSMIC X-RAY SOURCES
DECAY
DETECTION
EMISSION
ENERGY DEPENDENCE
IRON
LUMINOSITY
MASS
PHOTONS
REFLECTION
RELATIVISTIC RANGE
SPECTRA
STAR EVOLUTION
STARS
TELESCOPES
X RADIATION