On the Wolf-Rayet counterpart to IC 10 X-1

Abstract

Recent CHANDRA observations of the starburst galaxy IC 10 have resulted in an improved position for the bright (>10³⁸ erg s^-1) X-ray source IC 10 X-1. We discuss arguments in favour of the Wolf-Rayet star #17-A from Massey et al. and Crowther et al. being the optical counterpart; alternative possibilities are also considered. We discuss the properties of Massey et al. 17-A, finding it to be amongst the most luminous - and hence massive - WNE stars known and make comparisons with Cyg X-3. Finally we examine evolutionary constraints relating to the nature of the compact companion, finding that a putative neutron star companion would place stringent constraints on the minimum progenitor mass required to form a black hole in close binaries.