We present dedicated quasi-simultaneous X-ray ( Swift ) and optical ( Very Large Telescope ( VLT ) , V- and R-band ) observations of the intermediate mass black hole candidate ESO 243-49 HLX-1 ( catalog HLX-1 ) before and during the 2012 outburst .
We show that the V-band magnitudes vary with time , thus proving that a portion of the observed emission originates in the accretion disk .
Using the first quiescent optical observations of ESO 243-49 HLX-1 ( catalog HLX-1 ) , we show that the stellar population surrounding ESO 243-49 HLX-1 ( catalog HLX-1 ) is fainter than V \sim 25.1 and R \sim 24.2 .
We show that the optical emission may increase before the X-ray emission consistent with the scenario proposed by ( 19 ) in which the regular outbursts could be related to the passage at periastron of a star circling the intermediate mass black hole in an eccentric orbit , which triggers mass transfer into a quasi-permanent accretion disk around the black hole .
Further , if there is indeed a delay in the X-ray emission we estimate the mass-transfer delivery radius to be \sim 10 ^ { 11 } cm .