Monitoring the Enigmatic Behavior of the Supernova Impostor 2010da a.k.a. NGC 300 ULX1

Since its discovery, the behavior of the impostor supernova (SN) 2010da has continued to defy our understanding. Its dusty nature and variable IR behavior highlight the importance of continued IR monitoring with Spitzer/IRAC, and Spitzer is the only observatory sensitive enough to detected its mid-IR emission. SN2010da was discovered as a low-luminosity optical transient in the nearby galaxy NGC 300. After its outburst, SN2010da did not fade away but instead re-brightened at optical, infrared, and X-ray wavelengths to levels higher than its red and dusty progenitor. In addition to its strange transient behavior, recent X-ray studies revealed ultraluminous emission (LX >10^39 erg s-1) and a 30-second pulsation period. SN2010da, now dubbed NGC 300 ULX-1, has become the fourth example of the new class of Ultraluminous X-ray Sources (ULXs) that host pulsars emitting far above their Eddington limit. X-ray non-detections of its progenitor suggest the intriguing hypothesis that the 2010 outburst triggered the onset of super-Eddington accretion and ULX emission. The enigmatic behavior of SN2010da/NGC 300 ULX1 presents a unique opportunity for us to understand the accretion and mass exchange/loss in binary systems linked to the formation of a ULX. In this Spitzer DDT proposal, we request a total of 2.9 hrs to perform 6 observations of NGC 300 ULX1 at a weekly cadence during its upcoming visibility window in late 2019 to decipher the nature of its mid-IR/X-ray variability with coordinated observations with Swift/XRT. This would be our final chance to monitor the enigmatic mid-IR behavior of this mysterious SN impostor-turned ULX.