094461

We propose a 120 ks XMM-Newton observation to identify the nature of a ULX inthe metal-poor galaxy I Zw 18. In timing analysis we perform a pulse search todetermine whether it is a neutron star. Exploration of quasi-periodicoscillation and flat-topped noise in a power spectrum allows us to distinguishbetween a stellar-mass black hole and an intermediate-mass black hole (IMBH).Even if no such structures are found spectral analysis can distinguish betweena stellar-mass compact object in supercritical accretion and an IMBH insub-Eddington accretion. The I Zw 18 ULX in the lowest metallicity environmentis one of the best candidates for an IMBH. Determining the nature of the IZw18ULX is essential for delving into the evolution of binary systems. [truncated! Please see actual data for full text]