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We present dedicated quasi-simultaneous X-ray (Swift) and optical (Very LargeTelescope (VLT), V- and R-band) observations of the intermediate mass blackhole candidate ESO 243-49 HLX-1 before and during the 2012 outburst. We showthat the V-band magnitudes vary with time, thus proving that a portion of theobserved emission originates in the accretion disk. Using the first quiescentoptical observations of HLX-1, we show that the stellar population surroundingHLX-1 is fainter than V~25.1 and R~24.2. We show that the optical emission mayincrease before the X-ray emission consistent with the scenario proposed byLasota et al. (2011) in which the regular outbursts could be related to thepassage at periastron of a star circling the intermediate mass black hole in aneccentric orbit, which triggers mass transfer into a quasi-permanent accretiondisk around the black hole. Further, if there is indeed a delay in the X-rayemission we estimate the mass-transfer delivery radius to be ~1e11 cm.

Optical variability of the accretion disk around the intermediate mass black hole ESO 243-49 HLX-1 during the 2012 outburst