An Ultra-Luminous X-Ray Source with a Period of 55 Days

A new ultraluminous Xrays source (ULX) was recently discovered with Swift inNGC 6643. 200 days of Swift XRT coverage revealed an apparently periodic riseand fall of the Xray flux with a period of around 55 days. Only two otherperiodic ULXs are know to date. We propose five 10 ks XMMNewton EPICobservations to confirm and measure the period with high precision, needed toderive the mass of the mass donating object, and to study spectral changes atdifferent phases to investigate changes in the accretion process. Together withour existing Swift XRT, Chandra ACIS, VLA radio and Keck UBRI data, theXMMNewton observations will invigorate discussions about the nature of ULXs andwhether these enigmatic sources are due to accreting black holes are superEddington neutron stars. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]