Broadband Constraints on the Nature of NGC5055 ULX1

The ultraluminous Xray source population is now broadly expected to bedominated by superEddington accretors, thanks to the broadband spectroscopyprovided by XMM and NuSTAR in combination, the detection of Xray pulsationsfrom a growing subset of ULXs (unambiguously confirming them as superEddingtonneutron stars) and the detection of powerful outflows from a handful of systems.NGC5055 ULX1 is an extreme ULX (L(X,peak) virgul 1e40 erg/s) that has received verylittle observational attention to date. Here, we proposal a deep, coordinatedXMM+NuSTAR observation (130+150ks exposures, respectively) in order to constrainits broadband spectrum, search for pulsations, and atomic outflow signatures.These observations will provide the first robust constraints on the nature of this extreme binary truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]