Now this is what I haven't written in the post before, since I wasn't sure. I know that it would be dangerous, but just how dangerous? I took a look and it seems it has been proposed that a supernova explosion at the distance of roughly 100 light years away was the cause of Ordovician Extinction which killed 60% of species on Earth by depleting the ozone layer through chemical reactions in the atmosphere that were the aftermath of the explosion.
Further reading of this article says apparently in 1998 we were hit by gamma/x rays from supernova explosion 600 LY years away. So there definitely is a danger zone up to where? 300 LY? Another question: Would the explosion that is near enough to cause serious damage (as in, killing most people) be visible by observers BEFORE gamma and x rays do any visible damage?