Exploring the dramatic fading of SN2010da / NGC 300 ULX-1 with JWST

Over the last 12 years the enigmatic object SN 2010da / NGC 300 ULX-1 has continually defied expectation. Originally classified as a SN imposter, it was soon discovered that the system was extremely X-ray bright, indicative of a compact remnant accreting material from a donor star. It was recently discovered that the donor star in the system is a red supergiant (RSG) making NGC 300 ULX-1 the only known ULX pulsar with a cool supergiant companion. Over the last 4 years the RSG has faded dramatically across optical to near-IR wavelengths by around a factor of 10, and the molecular absorption features indicative of a cool supergiant can no longer be detected. This suggests either the system is returning to a quiescent state following the 2010 outburst or we are witnessing a never-before-seen RSG phase which cannot be explained by "standard" behaviours such as variability or quiescent winds, and may instead be indicative of the stars' impending death. As such ULX-1 represents a unique opportunity to probe eruptive mass-loss within an RSG-NS binary, and is a likely progenitor to either a compact object binary system or an elusive Thorne-Żytkow object. We are proposing to use NIRCam IFU and MIRI MRS to uncover the current state of ULX-1 and determine the most likely cause for the fading of the system. Ultimately this data will enable us to constrain the total mass lost in the system via either an eruptive outburst or interaction with the NS.