No Strong Geometric Beaming in the Ultraluminous Neutron Star Binary NGC 300 ULX-1 (SN 2010da) from Swift and Gemini

We have obtained near-simultaneous Swift/XRT imaging and Gemini GMOS spectroscopy for the ultraluminous X-ray source (ULX) NGC 300 ULX-1 (formerly designated SN 2010da). The observed X-ray emission is consistent with an inhomogeneous wind that partially obscures a central, bright inner accretion disk. We simultaneously fit eleven 0.3-10 keV spectra obtained over a similar to 1 year time period (2016 April to 2017 July) using the same partial covering model and find that although the covering fraction varies significantly (from 78% to consistent with 0%), the unabsorbed luminosity remains essentially constant across all observations ((2-6) x 10(39) erg s(-1)). A relatively high 0.3-10 keV fractional variability amplitude (F-var) of similar to 30% is observed in all 11 observations. Optical spectra from Gemini exhibit numerous emission lines (e.g., H alpha, H beta, He II lambda 4686), which suggest that the neutron star primary is photoionizing material in the immediate vicinity of the binary. We compare the He II lambda 4686 line luminosity (similar to(7-9) x 10(35) erg s(-1)) to the contemporaneous soft X-ray emission and find the X-ray emission is broadly consistent with the observed He II line luminosity. The combination of our X-ray observations and optical spectroscopy suggest that geometric beaming effects in the ULX-1 system are minimal, making ULX-1 one of only a few bona fide ULXs to be powered by accretion onto a neutron star.