A magnetar is the variant of a neutron star whose magnetic field is thousands of times stronger than that of a normal neutron star, equivalent to 1 billion gauss (for comparison, the Sun's magnetic field is about 5 gauss).
Magnetars erupt without warning, for hours or months, before starting to dim and eventually disappear.
Most of the known magnetars have been detected by X-ray telescopes in the wake of a high-energy burst, but they have also been observed emitting radio pulses very similar to those emitted by pulsars.
