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

HST spectrum and timing of the ultra-compact X-ray binary candidate 47 Tuc X9
HST spectrum and timing of the ultra-compact X-ray binary candidate 47 Tuc X9
To confirm the nature of the donor star in the ultra-compact X-ray binary candidate 47 Tuc X9, we obtained optical spectra (3,000$-$10,000 {\AA}) 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 $3\sigma$ upper limits on the H$\alpha$ and HeII $\lambda 4686$ emission line equivalent widths $-$EW$_{\mathrm{H\alpha}} \lesssim 14$ {\AA} and $-$EW$_{\mathrm{HeII}} \lesssim 9$ {\AA}, respectively. This is much lower than seen for typical X-ray binaries at a similar X-ray luminosity (which, for $L_{\mathrm{2-10 keV}} \approx 10^{33}-10^{34}$ erg s$^{-1}$ is typically $-$EW$_{\mathrm{H\alpha}} \sim 50$ {\AA}). This supports our previous suggestion (by Bahramian et al.) of an H-poor donor in X9. We perform timing analysis on archival far-ultraviolet, $V$ and $I$-band data to search for periodicities. In the optical bands we recover the seven-day 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.
astro-ph.HE, astro-ph.SR
0035-8711
1614-1623
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.
1f016b89-98b9-4fa9-8df0-9390fbb5eeda
Chomiuk, L.
71fe2d37-8846-4d13-8bcd-b8459a57aa93
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.
c8e0a8f1-20c1-404e-a55d-f7926e7fa7bc
Berg, M. van den
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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.
0de59032-c43c-4c8f-89a2-b451488b86db
Tudor, V.
329939d3-4583-4cd2-bda7-f2c95655be60
Miller-Jones, J.C.A.
3f659cec-bbb3-447c-b94e-4f170af560a6
Knigge, C.
ac320eec-631a-426e-b2db-717c8bf7857e
Maccarone, T.J.
c2f1d87b-e2ef-4e33-b09f-a2861d917ea8
Tauris, T.M.
25365808-30a5-4317-9616-8a39a36a8fe4
Bahramian, A.
1f016b89-98b9-4fa9-8df0-9390fbb5eeda
Chomiuk, L.
71fe2d37-8846-4d13-8bcd-b8459a57aa93
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.
588c7172-8fd8-4651-a8bf-6bbf72a36edd
Soria, R.
56ae49f7-b9b8-4eed-bae0-3947ea14ec19
Albrow, M.D.
5a1bf6e3-beeb-4a58-8941-8c519a4894df
Anderson, G.E.
c8e0a8f1-20c1-404e-a55d-f7926e7fa7bc
Berg, M. van den
a26a14f7-7078-4654-932f-0a31c2629263
Bernardini, F.
a24441f3-d18b-498e-b63a-5ab4498995ef
Bogdanov, S.
cffd0d0c-23dc-43ce-8be8-73ed32a16b9a
Britt, C.T.
1751cd59-4a8d-4eb7-9667-dc804fa3b095
Russell, D.M.
eaebc594-b18c-40f5-881b-c6028470c425
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., Berg, M. van den, Bernardini, F., Bogdanov, S., Britt, C.T., Russell, D.M. and Zurek, D.R. (2018) HST spectrum and timing of the ultra-compact X-ray binary candidate 47 Tuc X9. Monthly Notices of the Royal Astronomical Society, 476 (2), 1614-1623. (doi:10.1093/mnras/sty274).

Record type: Article

Abstract

To confirm the nature of the donor star in the ultra-compact X-ray binary candidate 47 Tuc X9, we obtained optical spectra (3,000$-$10,000 {\AA}) 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 $3\sigma$ upper limits on the H$\alpha$ and HeII $\lambda 4686$ emission line equivalent widths $-$EW$_{\mathrm{H\alpha}} \lesssim 14$ {\AA} and $-$EW$_{\mathrm{HeII}} \lesssim 9$ {\AA}, respectively. This is much lower than seen for typical X-ray binaries at a similar X-ray luminosity (which, for $L_{\mathrm{2-10 keV}} \approx 10^{33}-10^{34}$ erg s$^{-1}$ is typically $-$EW$_{\mathrm{H\alpha}} \sim 50$ {\AA}). This supports our previous suggestion (by Bahramian et al.) of an H-poor donor in X9. We perform timing analysis on archival far-ultraviolet, $V$ and $I$-band data to search for periodicities. In the optical bands we recover the seven-day 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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Accepted/In Press date: 1 February 2018
e-pub ahead of print date: 5 February 2018
Published date: May 2018
Additional Information: 20 pages, 12 figures. Accepted for publication in MNRAS
Keywords: astro-ph.HE, astro-ph.SR

Identifiers

Local EPrints ID: 418183
URI: http://eprints.soton.ac.uk/id/eprint/418183
ISSN: 0035-8711
PURE UUID: bf697387-5698-4884-814f-d6fb13605f36

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Date deposited: 23 Feb 2018 17:30
Last modified: 16 Dec 2019 18:25

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