A Magnetar is a Neutron Star with a strong Magnetic Field. The decay of the field powers Emission of X-rays and Gamma Rays. Star quakes can trigger gamma ray flashes i.e., the source of some longer Gamma-Ray Bursts.
Magnetars have been observed since 1979 and a theory was put forward in 1992. Circa 2013, 21 magnetars have been identified.