magnetar

A magnetar is a neutron star with a strong magnetic field (10¹³ to 10¹⁵ G). The decay of the field powers emission of X-rays and gamma rays. Starquakes may be triggered by the magnetic field and release a lot of magnetic field energy (magnetar flares, or for large ones, giant magnetar flares). Soft gamma repeaters (SGRs), which were first observed since 1979, have been modeled as magnetars since a 1992. Anomalous X-ray pulsars (AXPs) are also now interpreted to be magnetars. As of 2023, around 30 magnetars are known, along with a few candidates.

Magnetars are thought to have fairly short lifetimes, e.g., thousands of years, evolving to neutron stars no longer with the extreme magnetic fields. They are thought to have their strong field on formation, e.g., a core collapse supernova, or as the product of an neutron star merger. Though magnetic field strength grows as fields shrink, this is still thought to be insufficient to create the field strength of a magnetar, and the extra mechanism to do this is a topic of research. One notion is strengthening by a dynamo operating during the core collapse.

A a millisecond magnetar (MSM) is a magnetar that is also a millisecond pulsar (MSP).