Understanding state transitions in ULXs: wind spectroscopy of ULX bright states

In recent work done with XMMNewton, we have discovered that ultraluminous Xraysources (ULXs) have powerful winds in agreement with theoretical predictions ofsuperEddington accretion. Such winds vary on short timescales and cantemporarily block and reprocess the disc Xray photons, thus changing thespectral shape of the source. Enhanced Xray variability is seen during ULXhighest states including flux dips in soft ULXs and flares in hard ones,possibly due to a variable wind in our line of sight. We propose to test this,by studying the hard NGC 4559 X7 and the soft NGC 55 ULX1. 130ks XMMNewtonobservation per object triggered during a high state will enable us to performtime/fluxresolved Xray spectroscopy and probe the transition between soft, intermediate, and hard states. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]