Program: GN-2021B-FT-115

We request ~2hrs of GMOS long-slit spectra of IC 10 X-1, contemporaneous with an upcoming HST and Swift/Chandra observing campaign scheduled for November and January. This system is a black hole+Wolf-Rayet (BH+WR) high mass X-ray binary with an orbital period of 34.9 hrs. The BH mass is currently not well constrained, as the BH accretion disk irradiates the WR wind and alters the ionization structure of spectral line formation regions near the WR star. This alteration of the WR wind geometry masquerades as the classic binary RV curve. This effect is seen in the bright emission line due to He II 4686. To determine the BH mass, we need to look for emission lines from heavier elements (eg. C IV, N IV, etc.). We have been granted 10 orbits with Hubble/COS to obtain a phase-resolved FUV spectra, a 30 ks exposure with Chandra, and a Swift/XRT/UVOT snapshot monitoring campaign of IC 10 X-1 with the dual goals of determining a precise mass function of the BH and understanding the complex ionization structure imposed in the stellar wind by the radiation field of the accreting black hole. However, past studies have revealed a correlation between optical line profile and X-ray state of the BH in IC 10 X-1. This Gemini proposal targets the visible band, and is necessary to ensure that the geometry of the system remains stable (e.g., no significant changes in the WR wind properties or BH accretion disk structure) during the contemporaneous FUV and X-ray observations. Only ~3-6 WR+BH binaries are currently known. Despite their rarity, WR+BH binaries are believed to be the main channel for producing double degenerate binary systems (e.g., BH+BH or BH+NS systems), which are the potential progenitors of gravitational wave sources. Thus, understanding how the binary components affect one another and how these systems evolve -- which depends strongly on the masses of the binary components -- is of paramount importance.