http://www.space.com/31295-sun-catastrophic-superflare-possible.html
http://solarphysics.livingreviews.org/Articles/lrsp-2011-6/articlese6.html

A study has shown that it is possible for the sun to produce a large solar flare that would potentially cause problems with our technological society by causing radio black outs. The research is supported by the observations of a superflare of a binary star 1500 light years away These flares are caused by high energy radiation.
Stellar flares are similar to solar flares. They are both believed to be caused by magnetic reconnection.  The distribution of temperature and total energy is much larger.  A connection between temperature and emission measured can be found.

this equation can be derived from