Magnetars are rotating, highly magnetized
neutron stars.
They were first observed on August 17, 1997, as a burst
of
gamma rays and
x-rays, lasting about five minutes,
and it was so powerful that noticable
ionization in the
Earth's upper
atmosphere was recorded, in amounts that
compete with our
Sun's
radiation during daytime.
These bursts are due to earthquakes, or rather starquakes,
on the star's surface due to fluctuations in the extreme
magnetic field, causing the surface to crack open and
release a shower of high energy particles and gamma rays.
It is thought that magnetars can have a magnetic field
perhaps as strong as one million billion times the Earth's.