The size of the Vela SN remnant is
The Vela SN was only 800 light years away.
And there was another SN there, Vela Junior, that was visible in 1250 AD.
Did the aborigines leave a record of it?
http://en.wikipedia.org/wiki/Vela_Supernova_Remnant
http://en.wikipedia.org/wiki/RX_J0852.0-4622