The Long-Term Evolution of the ULX Pulsars NGC7793 P13 and NGC5907 ULX1

Since the discovery of the first pulsating ultraluminous X-ray source (ULX) in 2014, extensive effort has been invested in trying to understand these enigmatic neutron star X-ray binaries. Six ULX pulsars are now robustly confirmed, revealing extreme systems that appear to be able to exceed their Eddington limits by factors of up to ~500 (or more). Two of the best studied cases are NGC7793 P13 (peak L_X/L_edd ~ 100) and NGC5907 (peak L_X/L_edd ~ 500), each of which has received particularly significant observational investment from XMM-Newton, NuSTAR and Swift. I will present results on the long-term evolution of each of these systems from our recent monitoring campaigns combining all of these facilities, focusing in particular on what we can learn from the evolution of the neutron star spin.