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

TL;DR

This study identifies a 34.4-hour orbital period in the Wolf-Rayet X-ray binary IC 10 X-1, providing dynamic evidence that the compact object is a very massive stellar black hole, likely accreting from stellar wind.

Contribution

First detection of the orbital period and mass function in IC 10 X-1, confirming the black hole nature and its high mass compared to known stellar black holes.

Findings

Orbital period of 34.4 hours established.

Mass of the black hole estimated at 24-36 solar masses.

Binary is likely detached, accreting wind rather than Roche lobe overflow.

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.