The Complex Accretion Geometry of GX 339-4 as Seen by NuSTAR and Swift

Journal
Date Issued
2015
Author(s)
Fürst, F.
•
Nowak, M. A.
•
Tomsick, J. A.
•
Miller, J. M.
•
Corbel, S.
•
•
Boggs, S. E.
•
Christensen, F. E.
•
Craig, W. W.
•
Fabian, A. C.
•
Gandhi, P.
•
Grinberg, V.
•
Hailey, C. J.
•
Harrison, F. A.
•
Kara, E.
•
Kennea, J. A.
•
Madsen, K. K.
•
Pottschmidt, K.
•
Stern, D.
•
Walton, D. J.
•
Wilms, J.
•
Zhang, W. W.
DOI
Description
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.
Abstract
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\gt 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.
Volume
808
Issue
2
Start page
122
Uri
Url
Issn Identifier
0004-637X
Ads BibCode
2015ApJ...808..122F
Rights
open.access
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