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Durham University

Department of Physics

Staff profile

Publication details for Prof Tim Roberts

Prestwich, A. H., Kilgard, R., Crowther, P. A., Carpano, S., Pollock, A. M. T., Zezas, A., Saar, S. H., Roberts, T. P. & Ward, M. J. (2007). The Orbital Period of the Wolf-Rayet Binary IC 10 X-1: Dynamic Evidence that the Compact Object Is a Black Hole. Astrophysical Journal 669(1): L21-24.

Author(s) from Durham

Abstract

IC 10 X-1 is a bright (LX = 1038 ergs s-1) 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 Letter, we report on the detection of an X-ray orbital period for IC 10 X-1 of 34.4 hr. This result, combined with a reexamination of optical spectra, allows us to determine a mass function for the system of f(M) = 7.8 M☉ and a probable mass for the compact object of 24-33 M☉. If this analysis is correct, the compact object is the most massive stellar-mass black hole known. We further show that the observed period is inconsistent with Roche lobe overflow, suggesting that the binary is detached and that the black hole is accreting the wind of the Wolf-Rayet star. The observed mass-loss rate of [MAC92] 17A is sufficient to power the X-ray luminosity of IC 10 X-1.