The radio nebula of the ultra-luminous X-ray source NGC 5408 X-1

Ultra-luminous X-ray sources have higher apparent luminosities than Galactic stellar black holes and may be stellar black holes with beamed radiation or intermediate-mass black holes. We detected radio emission from an ultraluminous X-ray source in the dwarf irregular galaxy NGC 5408. We propose to use the ATCA to measure the radio spectrum of the nebula up to 18.5 Ghz (with the new CABB upgrade) allowing a much better estimate of its energy budget in order to test if the likely associated nebula could be inflated by a very massive black hole of several hundreds of solar masses