Tracking the Neutron Star ULX NGC 7793 P13 with XMM-Newton and NuSTAR

Following a series of remarkable recent discoveries, we now know that some ofthe most luminous members of the ultraluminous Xray source (ULX) population areactually powered by apparently superEddington neutron star accretors. Threesuch systems are now known: M82 X2, NGC7793 P13, and NGC5907 ULX1. Here wepropose a series of XMMNewton observations of P13, two of which will becoordinated with NuSTAR, in order to track the evolution of the pulse period,test the proposed orbital nature of the 64d optical period, and investigatechanges in both the average and the pulsephase resolved emission as a functionof flux, for comparison with the broader ULX population. Out of the three ULXpulsars currently known, the low absorption and lack of source confusion make P13 the ideal candidate for this study. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]