THE SOFT STATE OF CYGNUS X-1 OBSERVED WITH NuSTAR: A VARIABLE CORONA AND A STABLE INNER DISK
We present a multi-epoch hard X-ray analysis of Cygnus X-1 in its soft state based on four observations with the Nuclear Spectroscopic Telescope Array (NuSTAR). Despite the basic similarity of the observed spectra, there is clear spectral variability between epochs. To investigate this variability,...
| Main Authors: | , , , , , , , , , , , , , , , , , , , |
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| Format: | Article |
| Language: | en_US |
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IOP Publishing
2016
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| Online Access: | http://hdl.handle.net/1721.1/106131 https://orcid.org/0000-0003-2538-0188 |
| _version_ | 1826195260520267776 |
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| author | Walton, D. J. Tomsick, J. A. Madsen, K. K. Barret, D. Boggs, S. E. Christensen, F. E. Clavel, M. Craig, W. W. Fabian, A. C. Fuerst, F. Hailey, C. J. Harrison, F. A. Miller, J. M. Parker, M. L. Rahoui, F. Stern, D. Tao, L. Wilms, J. Zhang, W. Grinberg, Victoria |
| author2 | MIT Kavli Institute for Astrophysics and Space Research |
| author_facet | MIT Kavli Institute for Astrophysics and Space Research Walton, D. J. Tomsick, J. A. Madsen, K. K. Barret, D. Boggs, S. E. Christensen, F. E. Clavel, M. Craig, W. W. Fabian, A. C. Fuerst, F. Hailey, C. J. Harrison, F. A. Miller, J. M. Parker, M. L. Rahoui, F. Stern, D. Tao, L. Wilms, J. Zhang, W. Grinberg, Victoria |
| author_sort | Walton, D. J. |
| collection | MIT |
| description | We present a multi-epoch hard X-ray analysis of Cygnus X-1 in its soft state based on four observations with the Nuclear Spectroscopic Telescope Array (NuSTAR). Despite the basic similarity of the observed spectra, there is clear spectral variability between epochs. To investigate this variability, we construct a model incorporating both the standard disk-corona continuum and relativistic reflection from the accretion disk, based on prior work on Cygnus X-1, and apply this model to each epoch independently. We find excellent consistency for the black hole spin and the iron abundance of the accretion disk, which are expected to remain constant on observational timescales. In particular, we confirm that Cygnus X-1 hosts a rapidly rotating black hole, 0.93 ≲ a* ≲ 0.96, in broad agreement with the majority of prior studies of the relativistic disk reflection and constraints on the spin obtained through studies of the thermal accretion disk continuum. Our work also confirms the apparent misalignment between the inner disk and the orbital plane of the binary system reported previously, finding the magnitude of this warp to be ~10°–15°. This level of misalignment does not significantly change (and may even improve) the agreement between our reflection results and the thermal continuum results regarding the black hole spin. The spectral variability observed by NuSTAR is dominated by the primary continuum, implying variability in the temperature of the scattering electron plasma. Finally, we consistently observe absorption from ionized iron at ~6.7 keV, which varies in strength as a function of orbital phase in a manner consistent with the absorbing material being an ionized phase of the focused stellar wind from the supergiant companion star. |
| first_indexed | 2024-09-23T10:10:14Z |
| format | Article |
| id | mit-1721.1/106131 |
| institution | Massachusetts Institute of Technology |
| language | en_US |
| last_indexed | 2024-09-23T10:10:14Z |
| publishDate | 2016 |
| publisher | IOP Publishing |
| record_format | dspace |
| spelling | mit-1721.1/1061312022-09-30T19:21:30Z THE SOFT STATE OF CYGNUS X-1 OBSERVED WITH NuSTAR: A VARIABLE CORONA AND A STABLE INNER DISK Walton, D. J. Tomsick, J. A. Madsen, K. K. Barret, D. Boggs, S. E. Christensen, F. E. Clavel, M. Craig, W. W. Fabian, A. C. Fuerst, F. Hailey, C. J. Harrison, F. A. Miller, J. M. Parker, M. L. Rahoui, F. Stern, D. Tao, L. Wilms, J. Zhang, W. Grinberg, Victoria MIT Kavli Institute for Astrophysics and Space Research Grinberg, Victoria We present a multi-epoch hard X-ray analysis of Cygnus X-1 in its soft state based on four observations with the Nuclear Spectroscopic Telescope Array (NuSTAR). Despite the basic similarity of the observed spectra, there is clear spectral variability between epochs. To investigate this variability, we construct a model incorporating both the standard disk-corona continuum and relativistic reflection from the accretion disk, based on prior work on Cygnus X-1, and apply this model to each epoch independently. We find excellent consistency for the black hole spin and the iron abundance of the accretion disk, which are expected to remain constant on observational timescales. In particular, we confirm that Cygnus X-1 hosts a rapidly rotating black hole, 0.93 ≲ a* ≲ 0.96, in broad agreement with the majority of prior studies of the relativistic disk reflection and constraints on the spin obtained through studies of the thermal accretion disk continuum. Our work also confirms the apparent misalignment between the inner disk and the orbital plane of the binary system reported previously, finding the magnitude of this warp to be ~10°–15°. This level of misalignment does not significantly change (and may even improve) the agreement between our reflection results and the thermal continuum results regarding the black hole spin. The spectral variability observed by NuSTAR is dominated by the primary continuum, implying variability in the temperature of the scattering electron plasma. Finally, we consistently observe absorption from ionized iron at ~6.7 keV, which varies in strength as a function of orbital phase in a manner consistent with the absorbing material being an ionized phase of the focused stellar wind from the supergiant companion star. United States. National Aeronautics and Space Administration (Smithsonian Astrophysical Observatory. Contract SV3-73016) 2016-12-22T19:18:02Z 2016-12-22T19:18:02Z 2016-07 2016-04 Article http://purl.org/eprint/type/JournalArticle 1538-4357 0004-637X http://hdl.handle.net/1721.1/106131 Walton, D. J. et al. “THE SOFT STATE OF CYGNUS X-1 OBSERVED WITH NuSTAR : A VARIABLE CORONA AND A STABLE INNER DISK.” The Astrophysical Journal 826.1 (2016): 87. © Copyright 2016 IOP Publishing https://orcid.org/0000-0003-2538-0188 en_US http://dx.doi.org/10.3847/0004-637x/826/1/87 The Astrophysical Journal Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. application/pdf IOP Publishing American Astronomical Society |
| spellingShingle | Walton, D. J. Tomsick, J. A. Madsen, K. K. Barret, D. Boggs, S. E. Christensen, F. E. Clavel, M. Craig, W. W. Fabian, A. C. Fuerst, F. Hailey, C. J. Harrison, F. A. Miller, J. M. Parker, M. L. Rahoui, F. Stern, D. Tao, L. Wilms, J. Zhang, W. Grinberg, Victoria THE SOFT STATE OF CYGNUS X-1 OBSERVED WITH NuSTAR: A VARIABLE CORONA AND A STABLE INNER DISK |
| title | THE SOFT STATE OF CYGNUS X-1 OBSERVED WITH NuSTAR: A VARIABLE CORONA AND A STABLE INNER DISK |
| title_full | THE SOFT STATE OF CYGNUS X-1 OBSERVED WITH NuSTAR: A VARIABLE CORONA AND A STABLE INNER DISK |
| title_fullStr | THE SOFT STATE OF CYGNUS X-1 OBSERVED WITH NuSTAR: A VARIABLE CORONA AND A STABLE INNER DISK |
| title_full_unstemmed | THE SOFT STATE OF CYGNUS X-1 OBSERVED WITH NuSTAR: A VARIABLE CORONA AND A STABLE INNER DISK |
| title_short | THE SOFT STATE OF CYGNUS X-1 OBSERVED WITH NuSTAR: A VARIABLE CORONA AND A STABLE INNER DISK |
| title_sort | soft state of cygnus x 1 observed with nustar a variable corona and a stable inner disk |
| url | http://hdl.handle.net/1721.1/106131 https://orcid.org/0000-0003-2538-0188 |
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