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Alternative explanations for extreme supersolar iron abundances inferred from the energy spectrum of Cygnus X-1

Alternative explanations for extreme supersolar iron abundances inferred from the energy spectrum of Cygnus X-1
Alternative explanations for extreme supersolar iron abundances inferred from the energy spectrum of Cygnus X-1
Here we study a 1–200 keV energy spectrum of the black hole binary Cygnus X-1 taken with NuSTAR and Suzaku. This is the first report of a NuSTAR observation of Cyg X-1 in the intermediate state, and the observation was taken during the part of the binary orbit where absorption due to the companion's stellar wind is minimal. The spectrum includes a multi-temperature thermal disk component, a cutoff power-law component, and relativistic and nonrelativistic reflection components. Our initial fits with publicly available constant density reflection models (relxill and reflionx) lead to extremely high iron abundances (>9.96 and ${10.6}_{-0.9}^{+1.6}$ times solar, respectively). Although supersolar iron abundances have been reported previously for Cyg X-1, our measurements are much higher and such variability is almost certainly unphysical. Using a new version of reflionx that we modified to make the electron density a free parameter, we obtain better fits to the spectrum even with solar iron abundances. We report on how the higher density (${n}_{e}=({3.98}_{-0.25}^{+0.12})\times {10}^{20}$ cm−3) impacts other parameters such as the inner radius and inclination of the disk.
0004-637X
Tomsick, John A.
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Parker, Michael L.
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García, Javier A.
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Yamaoka, Kazutaka
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Barret, Didier
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Chiu, Jeng-lun
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Clavel, Maïca
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Fabian, Andrew
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Fürst, Felix
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Gandhi, Poshak
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Grinberg, Victoria
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Miller, Jon M.
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Pottschmidt, Katja
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Walton, Dominic J.
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Tomsick, John A.
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Parker, Michael L.
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García, Javier A.
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Yamaoka, Kazutaka
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Barret, Didier
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Chiu, Jeng-lun
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Clavel, Maïca
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Fabian, Andrew
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Fürst, Felix
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Gandhi, Poshak
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Grinberg, Victoria
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Miller, Jon M.
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Pottschmidt, Katja
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Walton, Dominic J.
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Tomsick, John A., Parker, Michael L., García, Javier A., Yamaoka, Kazutaka, Barret, Didier, Chiu, Jeng-lun, Clavel, Maïca, Fabian, Andrew, Fürst, Felix, Gandhi, Poshak, Grinberg, Victoria, Miller, Jon M., Pottschmidt, Katja and Walton, Dominic J. (2018) Alternative explanations for extreme supersolar iron abundances inferred from the energy spectrum of Cygnus X-1. The Astrophysical Journal, 855 (1), [3]. (doi:10.3847/1538-4357/aaaab1).

Record type: Article

Abstract

Here we study a 1–200 keV energy spectrum of the black hole binary Cygnus X-1 taken with NuSTAR and Suzaku. This is the first report of a NuSTAR observation of Cyg X-1 in the intermediate state, and the observation was taken during the part of the binary orbit where absorption due to the companion's stellar wind is minimal. The spectrum includes a multi-temperature thermal disk component, a cutoff power-law component, and relativistic and nonrelativistic reflection components. Our initial fits with publicly available constant density reflection models (relxill and reflionx) lead to extremely high iron abundances (>9.96 and ${10.6}_{-0.9}^{+1.6}$ times solar, respectively). Although supersolar iron abundances have been reported previously for Cyg X-1, our measurements are much higher and such variability is almost certainly unphysical. Using a new version of reflionx that we modified to make the electron density a free parameter, we obtain better fits to the spectrum even with solar iron abundances. We report on how the higher density (${n}_{e}=({3.98}_{-0.25}^{+0.12})\times {10}^{20}$ cm−3) impacts other parameters such as the inner radius and inclination of the disk.

Text
ALTERNATIVE EXPLANATIONS FOR EXTREME SUPERSOLAR IRON ABUNDANCES INFERRED FROM THE - Accepted Manuscript
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Accepted/In Press date: 22 January 2018
e-pub ahead of print date: 27 February 2018
Published date: 2018

Identifiers

Local EPrints ID: 419019
URI: http://eprints.soton.ac.uk/id/eprint/419019
ISSN: 0004-637X
PURE UUID: 89eaf740-f436-40e6-8329-8ac18e4bcdd0
ORCID for Poshak Gandhi: ORCID iD orcid.org/0000-0003-3105-2615

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Date deposited: 28 Mar 2018 16:30
Last modified: 17 Dec 2019 01:34

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Contributors

Author: John A. Tomsick
Author: Michael L. Parker
Author: Javier A. García
Author: Kazutaka Yamaoka
Author: Didier Barret
Author: Jeng-lun Chiu
Author: Maïca Clavel
Author: Andrew Fabian
Author: Felix Fürst
Author: Poshak Gandhi ORCID iD
Author: Victoria Grinberg
Author: Jon M. Miller
Author: Katja Pottschmidt
Author: Dominic J. Walton

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