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| Authors | J. Casares, C. Zurita, T. Shahbaz, P.A. Charles, R.P. Fender | | Title | Evidence of a Black Hole in the X-Ray Transient GS 1354-64 (=BW Circini) |
| Journal | Astrophysical Journal |
| Volume | 613 |
| Year | 2004 |
| Pages | L133-L136 |
| ISSN | 0004637X |
| Faculty | Faculty of Science |
| Institute/dept. | FNWI: Astronomical Institute Anton Pannekoek (IAP) |
| Keywords | - |
| Abstract | We present the first radial velocity curve of the companion star to BW Cir that demonstrates the presence of a black hole in this X-ray transient that recorded outbursts in 1987 and 1997 (and possibly 1971-1972). We identify weak absorption features corresponding to a G0-5 III donor star, strongly veiled by a residual accretion disk that contributes 61%-65% of the total light at 6300 ?. The Doppler motions of these features trace an orbit of P=2.54448 days (or its 1 yr alias of P=2.56358 days) and a velocity semiamplitude K<SUB>2</SUB>=279+/-5 km s<SUP>-1</SUP> (or K<SUB>2</SUB>=292+/-5 km s<SUP>-1</SUP>). Both solutions are equally possible. The mass function implied by the shorter period solution is f(M)=5.75+/-0.30 M<SUB>solar</SUB>, which, when combined with the rotational broadening of the tidally locked companion (Vsini=71+/-4 km s<SUP>-1</SUP>), yields a compact object mass of M<SUB>1</SUB><LIM ALIGN="R"><OP>sin</OP><UL>3</UL></LIM>i=7.34+/-0.46 M<SUB>solar</SUB>. This is substantially above the mass of a neutron star under any standard equation of state of nuclear matter. The companion star is probably a G subgiant that has evolved off the main sequence in order to fill its Roche lobe. Remarkably, a distance of >=27 kpc is inferred by the companion's luminosity, and this is supported by the large observed systemic velocity (gamma=103+/-4 km s<SUP>-1</SUP>), which requires such a distance in order to be consistent with the Galactic rotation curve. |
| Note | ©2004 American Astronomical Society |
| Document type | Article |
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