What is a hypernova and have we observed any? Inspired by the question "What does it mean for a star to go nova or supernova? Can I safely observe these?", I am curious about what hypernovas are?

Have we observed any occurring, or the at least the after-effects?

Is there an upper limit of how large a stellar explosion can be?
A hypernova is just a really, really big supernova.  UMass has a (tacky designed) web page that explains it.


  A hypernova explosion typically has a mechanical energy output of ~ 10^53 ergs, or about a factor of 100 greater than a supernova.


Regarding aftereffect, the page says this:


  The age of the hypernova remnant NGC5471B is about 30 thousand years, while the age of MF83 is about 1 million years.


As best as I am able to determine, we have not had a chance to observe any hypernova candidates in the modern era, although APOD featured the same one as mentioned by UMass:



According to New Scientist, research suggest the upper limit to a star is about 150 solar masses. These are the stars that create the infamous supernovas.his is as derived from the Eddington Limit.  Although R136a1 is an example of a star at nearly double that.  It is believed that these monsters are what are responsible for hypernovas. There is much to be learned from these stellar monsters!