Typically, we only notice supernovae hours or days after they happen in the visible spectrum, and we can then point our telescopes at them. When they first explode, they emit a lot of x-rays, but x-ray telescopes tend to have small fields of view, so we never catch anything. This January, Alicia Soderberg at Princeton was looking at a month-old supernova with an x-ray telescope when she happened to notice an x-ray burst nearby: another supernova! The burst was only about 5 minutes long, but she immediately called up lots of other people to aim their telescopes there, and so a ton of people got to observe a supernova sooner than ever before. Bad Astronomy Blog has a great writeup. I'm stealing this image from him:
The top row is in the UV spectrum and the bottom is in x-ray. The crazy thing that some of the news articles mess up on is that the two rows show the same field of view. That's how bright the x-ray burst was. Crazy, no?
Oh, and I wasn't kidding about a lot of people getting in on the action of gawking at this supernova. Check out how many coauthors are listed at the Nature abstract. :) Update: My physicist friend corrects me: "Dude, that's a tiny group by particle physics standards." :P