I know I'm way late, but I did once work out what kills you if your star goes supernova (type II anyway) while doing my dissertation on supernova physics. It's the neutrinos, as previously mentioned. They emerge from the center of the star several hours before there is any other outward sign of a problem. Any planet in a roughly 1 AU orbit will absorb enough energy from the neutrino blast to melt the entire planet into liquid rock, and this will happen pretty much instantly, everywhere. Needless to say, when the light hits, the planet absorbs photons much more efficiently, and the whole thing turns to vapor, but everyone is very very very dead long before then.