Definitely not a supernova - all bright stars are relatively close to us in galactic terms no matter how big or luminous they might be and if one went supernova it would become the most brilliant star in the night sky by many orders of magnitude, not dim out. Blinding! Supernovae don't just flash on either, there is a build-up to peak brightness. They can take months to fade away.
Still the odd bright (naked-eye) satellite winking out as it hits the Earth's shadow at that time but I couldn't find a match for Melbourne at 12:09 in Heavens Above. They had a mag 2.9 satellite winking out at about midnight and one at mag 3.2 winking out at around 12:30. Lots of things it could be - helicopter turning searchlight off or swinging it slowly out of view, etc etc.
Probably not Ric - evening cut-off time for Iridium flares at Melb at this time of year seems to be around 11pm. Could be some higher-orbit satellite flare a little later though.
