Magnetars are young and highly magnetized neutron stars that display a wide array of X-ray activity including short bursts, large outbursts, giant flares, and quasi-periodic oscillations, often coupled with interesting timing behavior including enhanced spin-down, glitches, and antiglitches. The bulk of this activity is explained by the evolution and decay of an ultrastrong magnetic field, stressing and breaking the neutron-star crust, which in turn drives twists of the external magnetosphere and powerful magnetospheric currents. The population of detected magnetars has grown to about 30 objects and shows unambiguous phenomenological connection with highly magnetized radio pulsars. Recent progress in magnetar theory includes explanation of the hard X-ray component in the magnetar spectrum and development of surface heating models, explaining the sources’ remarkable radiative output.

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