The December 27, 2004, outburst from the magnetic neutron star SGR
1806-20, _50,000 LY distant_, had an impact zone that included the
Earth...

Chris L Peterson:
The OP didn't define "impact zone". Brian chose to take it as the radius
where there would be significant biological impact on planets with
atmospheres. You've adopted a less extreme definition. Of course, one
could easily argue that any place where a supernova is detectable is
inside the impact zone.

Brian Tung:
Yes, that's right. I really didn't know what was meant by "impact zone"
in the original post. The least arbitrary meaning I came up with, given
the context that we are, after all, human beings asking the question,
was the one I used.

Just to be perfectly clear: it wasn't my intention to criticize Mr.
Tung's response in any way, but only to point out the remarkable power
of the SGR 1806-20 outburst. I find it remarkable that, at 50,000 LY,
it had an effect that was detectable not only by specialized detectors
on earth satellites, but by anyone who listens to short-wave radio
broadcasts -- quite a few millions of people around the world, in spite
of the advent of satellites and the Internet!

Davoud