Pulsations and constraints on time lags in two distinct ULXs: NGC 5204 X-1 and NGC 55 ULX-1

The nature of ultra-luminous X-ray sources (ULXs) is shrouded in mystery as they're believed to be point sources with luminosities above the classical Eddington limit for a 10$M_{\odot}$ black hole (BH), but generally fit into the classification tree of super-Eddington X-ray binaries. Studies of rev