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The complex accretion geometry of GX 339-4 as seen by NuSTAR and Swift

Fürst, F. and Nowak, M. A. and Tomsick, J. A. and Miller, J. M. and Corbel, S. and Bachetti, M. and Boggs, S. E. and Christensen, F. E. and Craig, W. W. and Fabian, A. C. and Gandhi, P. and Grinberg, V. and Hailey, C. J. and Harrison, F. A. and Kara, E. and Kennea, J. A. and Madsen, K. K. and Pottschmidt, K. and Stern, D. and Walton, D. J. and Wilms, J. and Zhang, W. W. (2015) The complex accretion geometry of GX 339-4 as seen by NuSTAR and Swift. Astrophysical Journal, 808 (2). Art. No. 122. ISSN 0004-637X.

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We present spectral analyses of five Nuclear Spectroscopic Telescope Array and Swift observations of GX 339–4 taken during a failed outburst during the summer of 2013. These observations cover Eddington luminosity fractions in the range ≈0.9%–6%. Throughout this outburst GX 339–4 stayed in the hard state and all five observations show similar X-ray spectra, with a hard power law with a photon index near 1.6, and significant contribution from reflection. Using simple reflection models we find unrealistically high iron abundances. Allowing for different photon indices for the continuum incident on the reflector relative to the underlying observed continuum results in a statistically better fit and reduced iron abundances. With a photon index around 1.3, the input power law on the reflector is significantly harder than that which is directly observed. We study the influence of different emissivity profiles and geometries and consistently find an improvement when using separate photon indices. The inferred inner accretion disk radius is strongly model dependent, but we do not find evidence for a truncation radius larger than 100 r_g in any model. The data do not allow independent spin constraints, but the results are consistent with the literature (i.e., a > 0). Our best-fit models indicate an inclination angle in the range 40°–60°, consistent with limits on the orbital inclination but higher than reported in the literature using standard reflection models. The iron line around 6.4 keV is clearly broadened, and we detect a superimposed narrow core as well. This core originates from a fluorescent region outside the influence of the strong gravity of the black hole. Additionally, we discuss possible geometries.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Bachetti, M.0000-0002-4576-9337
Boggs, S. E.0000-0001-9567-4224
Gandhi, P.0000-0003-3105-2615
Harrison, F. A.0000-0003-2992-8024
Madsen, K. K.0000-0003-1252-4891
Stern, D.0000-0003-2686-9241
Walton, D. J.0000-0001-5819-3552
Additional Information:© 2015 The American Astronomical Society. Received 2015 January 23; accepted 2015 June 4; published 2015 July 27. We thank the anonymous referee for very constructive and helpful comments. This work was supported under NASA Contract No. NNG08FD60C and made use of data from the NuSTAR mission, a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by the National Aeronautics and Space Administration. We thank the NuSTAR Operations, Software, and Calibration teams for support with the execution and analysis of these observations. This research has made use of the NuSTAR Data Analysis Software (NuSTARDAS), jointly developed by the ASI Science Data Center (ASDC, Italy) and the California Institute of Technology (USA). J.A.T. acknowledges partial support from NASA Swift Guest Investigator grants NNX13AJ81G and NNX14AC56G. S.C. acknowledges funding support from the ANR “CHAOS” (ANR-12-BS05-0009). We would like to thank John E. Davis for the slxfig module, which was used to produce all figures in this work.
Group:NuSTAR, Space Radiation Laboratory
Funding AgencyGrant Number
Agence Nationale pour la Recherche (ANR)ANR-12-BS05-0009
Subject Keywords:accretion, accretion disks – stars: black holes – X-rays: binaries – X-rays: individual (GX 339–4)
Other Numbering System:
Other Numbering System NameOther Numbering System ID
Space Radiation Laboratory2015-45
Record Number:CaltechAUTHORS:20150802-092749093
Persistent URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:59140
Deposited By: Joy Painter
Deposited On:06 Aug 2015 16:53
Last Modified:21 Mar 2019 18:58

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