What high-energy radiation bursts are caused by stresses on a magnetar's crust?

Soft gamma repeaters or anomalous X-ray pulsars

The immense magnetic field strength in a magnetar exerts significant stress upon the star's rigid outer crust. When this stress overcomes the crust's structural integrity, catastrophic fracturing occurs, leading to events known as starquakes. These starquakes release prodigious amounts of energy in the form of high-energy radiation. The specific designations for these energetic emissions, which are tied to the magnetic tension characteristic of the object, are soft gamma repeaters or anomalous X-ray pulsars. This phenomenon underscores that magnetic tension, rather than rotational energy alone, is the key characteristic driving the observed activity of these compact objects.