088396

In recent work done with XMM-Newton comma we have discovered that ultraluminous X-ray sources openParULXsclosePar have powerful winds in agreement with theoretical predictions of super-Eddington accretion. Such winds vary on short timescales and can temporarily block and reprocess the disc X-ray photons comma thus changing the spectral shape of the source. Enhanced X-ray variability is seen during ULX highest states including flux dips in soft ULXs and flares in hard ones comma possibly due to a variable wind in our line of sight. We propose to test this comma by studying the hard NGC 4559 X-7 and the soft NGC 55 ULX-1. 130ks XMM-Newton observation per object triggered during a high state will enable us to perform time--flux-resolved X-ray spectroscopy and probe the transition between soft comma intermediate comma and hard states.