A 'high-hard' outburst of the black hole X-ray binary GS 1354-64

K. I.I. Koljonen, D. M. Russell, J. M. Corral-Santana, M. Armas Padilla, T. Muñoz-Darias, F. Lewis, M. Coriat, E. Bauer

Research output: Contribution to journalArticlepeer-review


We study in detail the evolution of the 2015 outburst of GS 1354-64 (BW Cir) at optical, UV and X-ray wavelengths using Faulkes Telescope South/Las Cumbres Observatory Global Telescope Network, Small & Moderate Aperture Research Telescope System and Swift. The outburst was found to stay in the hard X-ray state, albeit being anomalously luminous with a peak luminosity of LX > 0.15 LEdd, which could be the most luminous hard state observed in a black hole X-ray binary. We found that the optical/UV emission is tightly correlated with the X-ray emission, consistent with accretion disc irradiation and/or a jet producing the optical emission. The X-ray spectra can be fitted well with a Comptonization model, and show softening towards the end of the outburst. In addition, we detect a QPO in the X-ray light curves with increasing centroid frequency during the peak and decay periods of the outburst. The long-term optical light curves during quiescence show a statistically significant, slow rise of the source brightness over the 7 years prior to the 2015 outburst. This behaviour as well as the outburst evolution at all wavelengths studied can be explained by the disc instability model with irradiation and disc evaporation/condensation.

Original languageEnglish (US)
Pages (from-to)942-955
Number of pages14
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
StatePublished - Jul 21 2016


  • Accretion, accretion discs
  • Binaries: close
  • X-rays: binaries
  • X-rays: individual: GS 1354-64
  • X-rays: stars

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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