Spaceflightnow is carrying this nifty "article and picture" of what may be the brightest supernova ever recorded:

We now know that SN 1006 heralded not the appearance of a new star, but the cataclysmic death of an old one located about 7,000 light years from Earth. It was likely a white dwarf star that had been pulling matter off an orbiting companion star. When the white dwarf mass exceeded the stability limit (known as the Chandrasekhar limit), it exploded.

I always thought these sorts of events were novas, while the event caused when a supermassive star destroys itself is a supernova. Ah well, must've been sleeping in astronomy class that day.