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

• Author(s) / Creator(s)

  • Tudor, Vlad
  • Miller-Jones, James C. A.
  • Knigge, C.
  • Maccarone, Thomas J.
  • Tauris, T. M.
  • Bahramian, Arash
  • Chomiuk, Laura
  • Heinke, Craig O.
  • Sivakoff, Gregory Robert
  • Strader, Jay
  • Plotkin, Richard M.
  • Soria, Roberto
  • Albrow, M. D.
  • Anderson, G. E.
  • van den Berg, Maureen
  • Bernardini, Federico
  • Bogdanov, Slavko
  • Britt, Christopher. T.
  • Russell, D. M.
  • Zurek, David R.

• 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 H α and He II λ4686 emission line equivalent widths − EWH α ≲ 14 Å and −EWHeII≲9 Å, respectively. This is much lower than seen for typical X-ray binaries at a similar X-ray luminosity (which, for L2--10keV≈1033--1034 erg s−1 is typically − EWH α ∼ 50 Å). 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 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.

• Date created

  2018-01-01

• Subjects / Keywords

  • Accretion Discs
  • Accretion
  • Stars: Black Holes
  • X-Rays: Binaries
  • Stars: Neutron

• Type of Item

  Article (Published)

• DOI

  https://doi.org/10.7939/r3-jzrt-fd06

• License

  This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.