Extreme ULXs: super-Eddington accretors comma or intermediate-mass black holes

Ultraluminous Xray sources with luminosities up to 2e40 erg/s are now regardedas likely superEddington accretors powered by stellar mass black holes, andthose above 1e41 erg/s may be good intermediatemass black hole (IMBH)candidates. However, the few objects lying between these ranges have anuncertain nature, and remain poorly studied. Here, we propose a new deepobservation of one such object located within 20 Mpc. We will use the highquality EPIC data to determine whether its spectrum shows the characteristicsignatures of the ultraluminous state, indicative of superEddington accretiononto large stellar black holes, or whether it appears consistent with the hardpowerlaw spectra and >10% fractional variability of an IMBH in the hard state. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]