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The ultracompact nature of the black hole candidate X-ray binary 47 Tuc X9

The ultracompact nature of the black hole candidate X-ray binary 47 Tuc X9
The ultracompact nature of the black hole candidate X-ray binary 47 Tuc X9
47 Tuc X9 is a low-mass X-ray binary (LMXB) in the globular cluster 47 Tucanae, and was previously thought to be a cataclysmic variable. However, Miller-Jones et al. recently identified a radio counterpart to X9 (inferring a radio/X-ray luminosity ratio consistent with black hole LMXBs), and suggested that the donor star might be a white dwarf. We report simultaneous observations of X9 performed by Chandra, NuSTAR and Australia Telescope Compact Array. We find a clear 28.18 ± 0.02-min periodic modulation in the Chandra data, which we identify as the orbital period, confirming this system as an ultracompact X-ray binary. Our X-ray spectral fitting provides evidence for photoionized gas having a high oxygen abundance in this system, which indicates a C/O white dwarf donor. We also identify reflection features in the hard X-ray spectrum, making X9 the faintest LMXB to show X-ray reflection. We detect an ∼6.8-d modulation in the X-ray brightness by a factor of 10, in archival Chandra, Swift and ROSAT data. The simultaneous radio/X-ray flux ratio is consistent with either a black hole primary or a neutron star primary, if the neutron star is a transitional millisecond pulsar. Considering the measured orbital period (with other evidence of a white dwarf donor), and the lack of transitional millisecond pulsar features in the X-ray light curve, we suggest that this could be the first ultracompact black hole X-ray binary identified in our Galaxy.
0035-8711
2199-2216
Bahramian, Arash
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Heinke, Craig O.
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Tudor, Vlad
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Miller-Jones, James C. A.
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Bogdanov, Slavko
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Maccarone, Thomas J.
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Knigge, Christian
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Sivakoff, Gregory R.
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Chomiuk, Laura
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Strader, Jay
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Garcia, Javier
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Kallman, Timothy
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Bahramian, Arash
390154f6-92b9-4e9f-9c5e-2eeaec97460a
Heinke, Craig O.
d7382ed2-cb85-4e15-b2d9-296fc8b6221d
Tudor, Vlad
2356f4cd-ccdb-4026-a7b6-bd5850d9caf7
Miller-Jones, James C. A.
cf33687c-452d-4d05-b0ef-ab9559afee59
Bogdanov, Slavko
39f20582-4d71-4b1a-ae2a-b266367341ef
Maccarone, Thomas J.
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Knigge, Christian
ac320eec-631a-426e-b2db-717c8bf7857e
Sivakoff, Gregory R.
e725b4eb-7437-46ca-9f6e-e56847938736
Chomiuk, Laura
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Strader, Jay
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Garcia, Javier
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Kallman, Timothy
0764a443-2cc6-4f87-98bc-82a06b386069

Bahramian, Arash, Heinke, Craig O., Tudor, Vlad, Miller-Jones, James C. A., Bogdanov, Slavko, Maccarone, Thomas J., Knigge, Christian, Sivakoff, Gregory R., Chomiuk, Laura, Strader, Jay, Garcia, Javier and Kallman, Timothy (2017) The ultracompact nature of the black hole candidate X-ray binary 47 Tuc X9. Monthly Notices of the Royal Astronomical Society, 467 (2), 2199-2216. (doi:10.1093/mnras/stx166).

Record type: Article

Abstract

47 Tuc X9 is a low-mass X-ray binary (LMXB) in the globular cluster 47 Tucanae, and was previously thought to be a cataclysmic variable. However, Miller-Jones et al. recently identified a radio counterpart to X9 (inferring a radio/X-ray luminosity ratio consistent with black hole LMXBs), and suggested that the donor star might be a white dwarf. We report simultaneous observations of X9 performed by Chandra, NuSTAR and Australia Telescope Compact Array. We find a clear 28.18 ± 0.02-min periodic modulation in the Chandra data, which we identify as the orbital period, confirming this system as an ultracompact X-ray binary. Our X-ray spectral fitting provides evidence for photoionized gas having a high oxygen abundance in this system, which indicates a C/O white dwarf donor. We also identify reflection features in the hard X-ray spectrum, making X9 the faintest LMXB to show X-ray reflection. We detect an ∼6.8-d modulation in the X-ray brightness by a factor of 10, in archival Chandra, Swift and ROSAT data. The simultaneous radio/X-ray flux ratio is consistent with either a black hole primary or a neutron star primary, if the neutron star is a transitional millisecond pulsar. Considering the measured orbital period (with other evidence of a white dwarf donor), and the lack of transitional millisecond pulsar features in the X-ray light curve, we suggest that this could be the first ultracompact black hole X-ray binary identified in our Galaxy.

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The Ultracompact nature of the black hole - Accepted Manuscript
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Accepted/In Press date: 18 January 2017
e-pub ahead of print date: 24 February 2017
Published date: 24 February 2017
Organisations: Astronomy Group

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Local EPrints ID: 407360
URI: https://eprints.soton.ac.uk/id/eprint/407360
ISSN: 0035-8711
PURE UUID: 8cd0a224-2fcd-406c-8922-19fff5082976

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Date deposited: 04 Apr 2017 01:07
Last modified: 13 Mar 2019 20:07

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Contributors

Author: Arash Bahramian
Author: Craig O. Heinke
Author: Vlad Tudor
Author: James C. A. Miller-Jones
Author: Slavko Bogdanov
Author: Thomas J. Maccarone
Author: Gregory R. Sivakoff
Author: Laura Chomiuk
Author: Jay Strader
Author: Javier Garcia
Author: Timothy Kallman

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