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Published September 1, 2016 | Submitted + Published
Journal Article Open

Spectro-Timing Study of GX 339-4 in a Hard Intermediate State


We present an analysis of Nuclear Spectroscopic Telescope Array observations of a hard intermediate state of the transient black hole GX 339−4 taken in 2015 January. With the source softening significantly over the course of the 1.3 day long observation we split the data into 21 sub-sets and find that the spectrum of all of them can be well described by a power-law continuum with an additional relativistically blurred reflection component. The photon index increases from ~1.69 to ~1.77 over the course of the observation. The accretion disk is truncated at around nine gravitational radii in all spectra. We also perform timing analysis on the same 21 individual data sets, and find a strong type-C quasi-periodic oscillation (QPO), which increases in frequency from ~0.68 to ~1.05 Hz with time. The frequency change is well correlated with the softening of the spectrum. We discuss possible scenarios for the production of the QPO and calculate predicted inner radii in the relativistic precession model as well as the global disk mode oscillations model. We find discrepancies with respect to the observed values in both models unless we allow for a black hole mass of ~100 M⊙, which is highly unlikely. We discuss possible systematic uncertainties, in particular with the measurement of the inner accretion disk radius in the relativistic reflection model. We conclude that the combination of observed QPO frequencies and inner accretion disk radii, as obtained from spectral fitting, is difficult to reconcile with current models.

Additional Information

© 2016 The American Astronomical Society. Received 2016 April 27; revised 2016 June 10; accepted 2016 June 28; published 2016 August 25. We thank the anonymous referee for the constructive and helpful comments. We thank the NuSTAR schedulers and SOC, in particular Karl Forster, for making this observation possible. We thank Javier García and Thomas Dauser for helpful discussions about the reflection models. 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. Support for this work was provided by NASA through the Smithsonian Astrophysical Observatory (SAO) contract SV3-73016 to MIT for Support of the Chandra X-ray Center (CXC) and Science Instruments; CXC is operated by SAO for and on behalf of NASA under contract NAS8-03060. 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). This research has made use of a collection of ISIS functions (ISISscripts) provided by ECAP/Remeis observatory and MIT (http://www.sternwarte.uni-erlangen.de/isis/). We would like to thank John E. Davis for the slxfig module, which was used to produce all figures in this work. This research has made use of MAXI data provided by RIKEN, JAXA and the MAXI team. Facility: NuSTAR - The NuSTAR (Nuclear Spectroscopic Telescope Array) mission.

Attached Files

Published - apj_828_1_34.pdf

Submitted - 1604.08644v2.pdf


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August 20, 2023
October 20, 2023