Verifying the intermediate mass black hole nature of the ultraluminous X-ray source HLX-1 associated with ESO 243-49

We request a deep radio observation of the new ultra luminous X-ray source HLX-1, with ATCA, to verify its intermediate mass black hole nature. The X-ray luminosity indicates a minimum black hole mass of 500 solar masses, alluding to a much sought after intermediate mass black hole. Radio observations will allow us to determine or at least allow us to place an upper limit on the mass to enable us to confirm the intermediate mass black hole nature. These observations will be made when the source transits between the low/hard state to the high/soft state. During these transitions, Galactic black hole binaries have been shown to exhibit radio flares that are a factor ten brighter than the non-flaring radio emission. This Target of Opportunity observation will be triggered using Swift weekly/bi-weekly observations that will reveal when the transition between the states occurs and provide us with the simultaneous X-ray observations necessary to constrain the mass. This is currently one of the best candidates for an intermediate mass black hole, the possible building blocks of supermassive black holes found in the centres of many galaxies.