Spectro-timing study of GX 339-4 in a hard intermediate state
- Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125 (United States)
- Massachusetts Institute of Technology, Kavli Institute for Astrophysics, Cambridge, MA 02139 (United States)
- Space Sciences Laboratory, University of California, Berkeley, CA 94720 (United States)
- INAF/Osservatorio Astronomico di Cagliari, I-09047 Selargius (Canada) (Italy)
- DTU Space, National Space Institute, Technical University of Denmark, DK-2800 Lyngby (Denmark)
- Department of Physics and Astronomy, University of Southampton, Highfield, Southampton SO17 1BJ (United Kingdom)
- Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027 (United States)
- Institute of Astronomy, Cambridge CB3 0HA (United Kingdom)
- CRESST, Department of Physics, and Center for Space Science and Technology, UMBC, Baltimore, MD 21250 (United States)
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States)
- Dr. Karl-Remeis-Sternwarte and ECAP, University of Erlangen-Nuremberg, D-96049 Bamberg (Germany)
- NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
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{sub ⊙}, 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.
- OSTI ID:
- 22868744
- Journal Information:
- Astrophysical Journal, Vol. 828, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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