Swift J1644+57 is streaming out radiation. It is thought that this is due to to a previously dormant black hole swallowing a star. [Very bad for the star ;-)]
And here is more information on the Type Ia supernova in M101.
And if you look here you will find some notes on how to observe it!
See Also: http://deadmanchatting.blogspot.com/2011/08/new-supernava.html