Subject: Why is the crab nebula still such a potent synchrotron source?

It is to my understanding that a cloud of electrons spiral around the crab 
nebulas magnetic field. They while accelerating in circular motion, emit 
electromagnetic radiation and so must lose kinetic energy because energy is 
conserved.The thing that puzzles me is that it has been over 900 years since 
it exploded and yet still emits more energy than the sun, meaning that the 
electrons must be getting a huge amount of energy from somewhere in order to 
be able to still emit photons in the visible region of the spectrum.
I came across this problem after reading "Cosmic Rays" by Michael W. 
Friedlander.

Re: Why is the crab nebula still such a potent synchrotron source?