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Broadband X-ray spectra of GX 339-4 and the geometry of accreting black holes in the hard state

Broadband X-ray spectra of GX 339-4 and the geometry of accreting black holes in the hard state
Broadband X-ray spectra of GX 339-4 and the geometry of accreting black holes in the hard state
A major question in the study of black hole binaries involves our understanding of the accretion geometry when the sources are in the "hard" state, with an X-ray energy spectrum dominated by a hard power-law component and radio emission coming from a steady "compact" jet. Although the common hard state picture is that the accretion disk is truncated, perhaps at hundreds of gravitational radii (Rg) from the black hole, recent results for the recurrent transient GX 339–4 by Miller and coworkers show evidence for disk material very close to the black hole's innermost stable circular orbit. That work studied GX 339–4 at a luminosity of ~5% of the Eddington limit (LEdd) and used parameters from a relativistic reflection model and the presence of a thermal component as diagnostics. Here we use similar diagnostics but extend the study to lower luminosities (2.3% and 0.8% LEdd) using Swift and RXTE observations of GX 339–4. We detect a thermal component with an inner disk temperature of ~0.2 keV at 2.3% LEdd. At both luminosities, we detect broad features due to iron Kα that are likely related to reflection of hard X-rays off disk material. If these features are broadened by relativistic effects, they indicate that the material resides within 10Rg, and the measurements are consistent with the disk's inner radius remaining at ~4Rg down to 0.8% LEdd. However, we also discuss an alternative model for the broadening, and we note that the evolution of the thermal component is not entirely consistent with the constant inner radius interpretation.
accretion, accretion disks, black hole physics, stars: individual (GX 339-4), x-rays: general, x-rays: stars
0004-637X
593
Tomsick, John A.
96b2e8cc-70c1-424a-8380-2551a5077ff5
Kalemci, Emrah
4fb7c67c-3eae-4956-9a93-ae65c5eebd86
Kaaret, Philip
590bc5e8-b6f9-433c-9408-b800eaf6ed15
Markoff, Sera
ed3a5fdb-0456-4fb3-8aa4-ee2f710f7029
Corbel, Stephane
7ef18014-6069-4111-a7f3-7ca6f17de84b
Migliari, Simone
6f3d123b-a4af-4d44-b1a2-6208d7b52dbc
Fender, Rob
c802ddfc-25a3-4c0e-899d-11c405c705d1
Bailyn, Charles D.
59295344-e9fb-47c5-b741-13a55c4788bd
Buxton, Michelle M.
ba14d6ff-6de0-40f7-8af2-cee734d6af6d
Tomsick, John A.
96b2e8cc-70c1-424a-8380-2551a5077ff5
Kalemci, Emrah
4fb7c67c-3eae-4956-9a93-ae65c5eebd86
Kaaret, Philip
590bc5e8-b6f9-433c-9408-b800eaf6ed15
Markoff, Sera
ed3a5fdb-0456-4fb3-8aa4-ee2f710f7029
Corbel, Stephane
7ef18014-6069-4111-a7f3-7ca6f17de84b
Migliari, Simone
6f3d123b-a4af-4d44-b1a2-6208d7b52dbc
Fender, Rob
c802ddfc-25a3-4c0e-899d-11c405c705d1
Bailyn, Charles D.
59295344-e9fb-47c5-b741-13a55c4788bd
Buxton, Michelle M.
ba14d6ff-6de0-40f7-8af2-cee734d6af6d

Tomsick, John A., Kalemci, Emrah, Kaaret, Philip, Markoff, Sera, Corbel, Stephane, Migliari, Simone, Fender, Rob, Bailyn, Charles D. and Buxton, Michelle M. (2008) Broadband X-ray spectra of GX 339-4 and the geometry of accreting black holes in the hard state. Astrophysical Journal, 680 (1), 593. (doi:10.1086/587797).

Record type: Article

Abstract

A major question in the study of black hole binaries involves our understanding of the accretion geometry when the sources are in the "hard" state, with an X-ray energy spectrum dominated by a hard power-law component and radio emission coming from a steady "compact" jet. Although the common hard state picture is that the accretion disk is truncated, perhaps at hundreds of gravitational radii (Rg) from the black hole, recent results for the recurrent transient GX 339–4 by Miller and coworkers show evidence for disk material very close to the black hole's innermost stable circular orbit. That work studied GX 339–4 at a luminosity of ~5% of the Eddington limit (LEdd) and used parameters from a relativistic reflection model and the presence of a thermal component as diagnostics. Here we use similar diagnostics but extend the study to lower luminosities (2.3% and 0.8% LEdd) using Swift and RXTE observations of GX 339–4. We detect a thermal component with an inner disk temperature of ~0.2 keV at 2.3% LEdd. At both luminosities, we detect broad features due to iron Kα that are likely related to reflection of hard X-rays off disk material. If these features are broadened by relativistic effects, they indicate that the material resides within 10Rg, and the measurements are consistent with the disk's inner radius remaining at ~4Rg down to 0.8% LEdd. However, we also discuss an alternative model for the broadening, and we note that the evolution of the thermal component is not entirely consistent with the constant inner radius interpretation.

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More information

Published date: 10 June 2008
Keywords: accretion, accretion disks, black hole physics, stars: individual (GX 339-4), x-rays: general, x-rays: stars

Identifiers

Local EPrints ID: 147287
URI: http://eprints.soton.ac.uk/id/eprint/147287
ISSN: 0004-637X
PURE UUID: 64551801-e73c-4204-83da-d03e463e2407

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Date deposited: 27 May 2010 15:16
Last modified: 14 Mar 2024 00:58

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Contributors

Author: John A. Tomsick
Author: Emrah Kalemci
Author: Philip Kaaret
Author: Sera Markoff
Author: Stephane Corbel
Author: Simone Migliari
Author: Rob Fender
Author: Charles D. Bailyn
Author: Michelle M. Buxton

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