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Spectro-timing study of GX 339-4 in a hard intermediate state

Spectro-timing study of GX 339-4 in a hard intermediate state
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 Msun, 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.
1538-4357
1-10
Fürst, F.
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Grinberg, V.
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Tomsick, J.A.
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Bachetti, M.
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Boggs, S.E.
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Brightman, M.
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Christensen, F.E.
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Craig, W.W.
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Gandhi, P.
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Grefenstette, B.
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Hailey, C.J.
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Harrison, F.A.
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Madsen, K.K.
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Parker, M.L.
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Pottschmidt, K.
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Stern, D.
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Walton, D.J.
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Wilms, J.
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Zhang, W.W.
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Fürst, F.
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Grinberg, V.
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Tomsick, J.A.
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Bachetti, M.
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Boggs, S.E.
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Brightman, M.
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Christensen, F.E.
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Craig, W.W.
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Gandhi, P.
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Grefenstette, B.
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Hailey, C.J.
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Harrison, F.A.
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Madsen, K.K.
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Parker, M.L.
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Pottschmidt, K.
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Stern, D.
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Walton, D.J.
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Wilms, J.
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Zhang, W.W.
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Fürst, F., Grinberg, V., Tomsick, J.A., Bachetti, M., Boggs, S.E., Brightman, M., Christensen, F.E., Craig, W.W., Gandhi, P., Grefenstette, B., Hailey, C.J., Harrison, F.A., Madsen, K.K., Parker, M.L., Pottschmidt, K., Stern, D., Walton, D.J., Wilms, J. and Zhang, W.W. (2016) Spectro-timing study of GX 339-4 in a hard intermediate state. The Astrophysical Journal, 828 (1), 1-10. (doi:10.3847/0004-637X/828/1/34).

Record type: Article

Abstract

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 Msun, 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.

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e-pub ahead of print date: 28 June 2016
Published date: 25 August 2016
Organisations: Astronomy Group

Identifiers

Local EPrints ID: 399896
URI: http://eprints.soton.ac.uk/id/eprint/399896
ISSN: 1538-4357
PURE UUID: 080f0741-9829-4384-8d55-5fcb31e2b7ca
ORCID for P. Gandhi: ORCID iD orcid.org/0000-0003-3105-2615

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Date deposited: 02 Sep 2016 10:34
Last modified: 17 Dec 2019 01:34

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Contributors

Author: F. Fürst
Author: V. Grinberg
Author: J.A. Tomsick
Author: M. Bachetti
Author: S.E. Boggs
Author: M. Brightman
Author: F.E. Christensen
Author: W.W. Craig
Author: P. Gandhi ORCID iD
Author: B. Grefenstette
Author: C.J. Hailey
Author: F.A. Harrison
Author: K.K. Madsen
Author: M.L. Parker
Author: K. Pottschmidt
Author: D. Stern
Author: D.J. Walton
Author: J. Wilms
Author: W.W. Zhang

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