IN A SERIES OF STUNNING DISCOVERIES SEVERAL NEUTRON-STAR-POWERED ULXS HAVE NOW BEEN DISCOVERED WHICH ALL APPEAR TO EXCEED THEIR EDDINGTON LUMINOSITIES BY FACTORS OF UP TO 100 CONFOUNDING THEORY. ONE EXPLANATION IS THAT MAGNETAR FIELD STRENGTHS ARE REQUIRED IN ORDER TO REDUCE THE ELECTRON SCATTERING CROSS SECTION THAT INHIBITS THE ACCRETION HOWEVER NO DIRECT MEASUREMENT OF THE MAGNETIC FIELD STRENGTH HAS BEEN MADE UNTIL NOW. WE HAVE RECENTLY DETECTED A STRONG ABSORPTION LINE AT 4.5 KE V IN THE CHANDRA SPECTRUM OF ULX-8 IN M51 WHICH WE INTERPRET AS A PROTON CYCLOTRON LINE PRODUCED BY THE STRONG MAGNETIC FIELD OF A NEUTRON STAR. THE ENERGY OF THE LINE IMPLIES THE MAGNETIC FIELD STRENGTH IS OF ORDER 1015 G WHICH IS AT THE HIGH END OF MAGNETAR FIELD STRENGTHS. THE ABSORPTION LINE WAS DETECTED DURING AN APPARENT BURSTING EPISODE FROM THE SOURCE WHERE THE LUMINOSITY PEAKED AT 1040 ERG S.1 HOWEVER NO PULSATIONS WERE DETECTED BY CHANDRA POSSIBLY DUE TO THE LONG READOUT TIME OF THE ACIS DETECTORS. ALL ARCHIVAL OBSERVATIONS WITH XMM-NEWTON WHICH HAS A MUCH SHORTER READOUT TIME ARE TOO SHORT AND OCCURRED WHILE THIS SOURCE WAS AT LOW FLUXES. THE LACK OF DETECTED PULSATIONS PRECLUDES US FROM MAKING INFERENCES FROM THIS APPARENT MAGNETAR TO THE WIDER NEUTRON STAR ULX POPULATION. WE THEREFORE PROPOSE A DEEP OBSERVATION WITH XMM-NEWTON OF M51 IN ORDER TO SEARCH FOR PULSATIONS. M51 ALSO HAS A DIVERSE POPULATION OF OTHER ULXS FROM WHICH WE CAN SEARCH FOR PULSATIONS THAT WILL ALLOW US TO DRAW INFERENCES ABOUT THE PROPORTION OF ULXS WHICH ARE POWERED BY NEUTRON STARS.