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Alternative Explanations for Extreme Supersolar Iron Abundances Inferred from the Energy Spectrum of Cygnus X-1

Tomsick, John A. and Parker, Michael L. and García, Javier A. and Yamaoka, Kazutaka and Barret, Didier and Chiu, Jeng-Lun and Clavel, Maïca and Fabian, Andrew and Fürst, Felix and Gandhi, Poshak and Grinberg, Victoria and Miller, Jon M. and Pottschmidt, Katja and Walton, Dominic J. (2018) Alternative Explanations for Extreme Supersolar Iron Abundances Inferred from the Energy Spectrum of Cygnus X-1. Astrophysical Journal, 855 (1). Art. No. 3. ISSN 1538-4357. doi:10.3847/1538-4357/aaaab1.

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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)) x 10^(20) cm^(−3)) impacts other parameters such as the inner radius and inclination of the disk.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Tomsick, John A.0000-0001-5506-9855
Parker, Michael L.0000-0002-8466-7317
García, Javier A.0000-0003-3828-2448
Barret, Didier0000-0002-0393-9190
Clavel, Maïca0000-0003-0724-2742
Fabian, Andrew0000-0002-9378-4072
Fürst, Felix0000-0003-0388-0560
Gandhi, Poshak0000-0003-3105-2615
Grinberg, Victoria0000-0003-2538-0188
Pottschmidt, Katja0000-0002-4656-6881
Walton, Dominic J.0000-0001-5819-3552
Additional Information:© 2018 American Astronomical Society. Received 2017 December 1. Accepted 2018 January 22. Published 2018 February 27. This work 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. 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 data obtained from the Suzaku satellite, a collaborative mission between the space agencies of Japan (JAXA) and the USA (NASA). J.A.T. acknowledges partial support from NuSTAR Guest Observer grant NNX15AV23G. A.C.F. acknowledges support from ERC Advanced Grant 340442. D.J.W. acknowledges support from STFC in the form of an Ernest Rutherford fellowship. J.A.T. thanks K. Hamaguchi for help with the XIS data reduction and T. Dauser, K. Koljonen, and A. Zoghbi for useful discussions. This research has made use of the MAXI data provided by RIKEN, JAXA, and the MAXI team.
Group:NuSTAR, Space Radiation Laboratory
Funding AgencyGrant Number
European Research Council (ERC)340442
Science and Technology Facilities Council (STFC)UNSPECIFIED
Subject Keywords:accretion, accretion disks; black hole physics; stars: individual (Cygnus X-1) ; X-rays: general; X-rays: stars
Issue or Number:1
Record Number:CaltechAUTHORS:20180227-133907106
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Official Citation:John A. Tomsick et al 2018 ApJ 855 3
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:84975
Deposited By: Ruth Sustaita
Deposited On:28 Feb 2018 01:10
Last Modified:15 Nov 2021 20:24

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