Constraining the nature of the companion star of the IMBH HLX-1

We found in 2009 a strong virgul10^4 Msun IMBH candidate, the hyper luminous Xraysource HLX1 in the outskirts of the ESO 24349 galaxy. We proposed that theIMBH is fed by mass transfer episodes when a WD donor passes at periapsis and istidally stripped, leading to Xray outbursts. We detected in previous XMMobservations of HLX1 faint unresolved Xray lines at 0.64, 0.88 & 0.98keV. Wepropose that they may be due to photoionization of nearby material by thecentral source. We request a 130ks XMM ToO to detect with a high significancesoft Xray lines when the source will be near its emission peak. Modeling of theRGS data with photoionization codes will help us put constraints on thephysical and dynamical properties of the emitting material around the BH. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]