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American Astronomical Society, Astrophysical Journal, 1(669), p. L21-L24, 2007

DOI: 10.1086/523755

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The Orbital Period of the Wolf-Rayet Binary IC 10 X-1; Dynamic Evidence that the Compact Object is a Black Hole

Journal article published in 2007 by A. H. Prestwich, R. Kilgard, P. A. Crowther ORCID, S. Carpano, A. M. T. Pollock, A. Zezas, S. H. Saar, T. P. Roberts ORCID, M. J. Ward
This paper is made freely available by the publisher.
This paper is made freely available by the publisher.

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Abstract

IC 10 X-1 is a bright (Lx=10^38 ergs/s) variable X-ray source in the local group starburst galaxy IC 10. The most plausible optical counterpart is a luminous Wolf-Rayet star, making IC 10 X-1 a rare example of a Wolf-Rayet X-ray binary. In this paper, we report on the detection of an X-ray orbital period for IC 10 X-1of 34.4 hours. This result, combined with a re-examination of optical spectra, allow us to determine a mass function for the system f(m)=7.8 Msun and a probable mass for the compact object of 24-36 Msun. If this analysis is correct, the compact object is the most massive known stellar black black hole. We further show that the observed period is inconsistent with Roche lobe overflow, suggesting that the binary is detached and the black hole is accreting the wind of the Wolf-Rayet star. The observed mass loss rate of [MAC92] 17-A is sufficient to power the X-ray luminosity of IC 10 X-1. ; Comment: Accepted for publication in ApJ Letters