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HST spectrum and timing of the ultracompact X-ray binary candidate 47 Tuc X9

HST spectrum and timing of the ultracompact X-ray binary candidate 47 Tuc X9
HST spectrum and timing of the ultracompact X-ray binary candidate 47 Tuc X9

To confirm the nature of the donor star in the ultracompact X-ray binary candidate 47 Tuc X9, we obtained optical spectra (3000-10 000 Å) with the Hubble Space Telescope/Space Telescope Imaging Spectrograph. We find no strong emission or absorption features in the spectrum of X9. In particular, we place 3σ upper limits on the Hα and He II λ4686 emission line equivalent widths - EW ≲ 14Å and -EWHe II ≲ 9Å, respectively. This is much lower than seen for typical X-ray binaries at a similar X-ray luminosity (which, for L2-10 keV ≈ 1033-1034 erg s-1 is typically -EW ~ 50 Å). This supports our previous suggestion, by Bahramian et al., of an H-poor donor in X9. We perform timing analysis on archival farultraviolet, V- and I-band data to search for periodicities. In the optical bands, we recover the 7-d superorbital period initially discovered in X-rays, but we do not recover the orbital period. In the far-ultraviolet, we find evidence for a 27.2 min period (shorter than the 28.2 min period seen in X-rays). We find that either a neutron star or black hole could explain the observed properties of X9. We also perform binary evolution calculations, showing that the formation of an initial black hole/He-star binary early in the life of a globular cluster could evolve into a present-day system such as X9 (should the compact object in this system indeed be a black hole) via mass-transfer driven by gravitational wave radiation.

Accretion, Accretion discs, Stars: black holes, Stars: neutron, X-rays: binaries
0035-8711
1889-1908
Tudor, V.
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Miller-Jones, J. C.A.
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Knigge, C.
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Maccarone, T. J.
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Tauris, T. M.
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Bahramian, A.
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Chomiuk, L.
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Heinke, C. O.
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Sivakoff, G. R.
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Strader, J.
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Plotkin, R. M.
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Soria, R.
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Albrow, M. D.
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Anderson, G. E.
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van den Berg, M.
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Bernardini, F.
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Bogdanov, S.
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Britt, C. T.
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Russell, D.M.
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Zurek, D. R.
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Tudor, V.
329939d3-4583-4cd2-bda7-f2c95655be60
Miller-Jones, J. C.A.
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Knigge, C.
ac320eec-631a-426e-b2db-717c8bf7857e
Maccarone, T. J.
c2f1d87b-e2ef-4e33-b09f-a2861d917ea8
Tauris, T. M.
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Bahramian, A.
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Chomiuk, L.
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Heinke, C. O.
50442ec4-8a45-4aa5-b425-28d0c896dc08
Sivakoff, G. R.
e725b4eb-7437-46ca-9f6e-e56847938736
Strader, J.
65549124-aafe-4b6e-a5cb-2ca8b2624843
Plotkin, R. M.
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Soria, R.
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Albrow, M. D.
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Anderson, G. E.
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van den Berg, M.
a26a14f7-7078-4654-932f-0a31c2629263
Bernardini, F.
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Bogdanov, S.
cffd0d0c-23dc-43ce-8be8-73ed32a16b9a
Britt, C. T.
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Russell, D.M.
50ca7be8-5f79-4eff-942c-5f0f832188d1
Zurek, D. R.
0de59032-c43c-4c8f-89a2-b451488b86db

Tudor, V., Miller-Jones, J. C.A., Knigge, C., Maccarone, T. J., Tauris, T. M., Bahramian, A., Chomiuk, L., Heinke, C. O., Sivakoff, G. R., Strader, J., Plotkin, R. M., Soria, R., Albrow, M. D., Anderson, G. E., van den Berg, M., Bernardini, F., Bogdanov, S., Britt, C. T., Russell, D.M. and Zurek, D. R. (2018) HST spectrum and timing of the ultracompact X-ray binary candidate 47 Tuc X9. Monthly Notices of the Royal Astronomical Society, 476 (2), 1889-1908. (doi:10.1093/MNRAS/STY284).

Record type: Article

Abstract

To confirm the nature of the donor star in the ultracompact X-ray binary candidate 47 Tuc X9, we obtained optical spectra (3000-10 000 Å) with the Hubble Space Telescope/Space Telescope Imaging Spectrograph. We find no strong emission or absorption features in the spectrum of X9. In particular, we place 3σ upper limits on the Hα and He II λ4686 emission line equivalent widths - EW ≲ 14Å and -EWHe II ≲ 9Å, respectively. This is much lower than seen for typical X-ray binaries at a similar X-ray luminosity (which, for L2-10 keV ≈ 1033-1034 erg s-1 is typically -EW ~ 50 Å). This supports our previous suggestion, by Bahramian et al., of an H-poor donor in X9. We perform timing analysis on archival farultraviolet, V- and I-band data to search for periodicities. In the optical bands, we recover the 7-d superorbital period initially discovered in X-rays, but we do not recover the orbital period. In the far-ultraviolet, we find evidence for a 27.2 min period (shorter than the 28.2 min period seen in X-rays). We find that either a neutron star or black hole could explain the observed properties of X9. We also perform binary evolution calculations, showing that the formation of an initial black hole/He-star binary early in the life of a globular cluster could evolve into a present-day system such as X9 (should the compact object in this system indeed be a black hole) via mass-transfer driven by gravitational wave radiation.

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More information

Accepted/In Press date: 31 January 2018
e-pub ahead of print date: 5 February 2018
Published date: 11 May 2018
Keywords: Accretion, Accretion discs, Stars: black holes, Stars: neutron, X-rays: binaries

Identifiers

Local EPrints ID: 423480
URI: http://eprints.soton.ac.uk/id/eprint/423480
ISSN: 0035-8711
PURE UUID: 42b88a29-016a-43b9-aa11-bd484c6d2463

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Date deposited: 24 Sep 2018 16:30
Last modified: 15 Jan 2020 17:45

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Contributors

Author: V. Tudor
Author: J. C.A. Miller-Jones
Author: C. Knigge
Author: T. J. Maccarone
Author: T. M. Tauris
Author: A. Bahramian
Author: L. Chomiuk
Author: C. O. Heinke
Author: G. R. Sivakoff
Author: J. Strader
Author: R. M. Plotkin
Author: R. Soria
Author: M. D. Albrow
Author: G. E. Anderson
Author: M. van den Berg
Author: F. Bernardini
Author: S. Bogdanov
Author: C. T. Britt
Author: D.M. Russell
Author: D. R. Zurek

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