Magnetars, a Cosmic Physics Laboratory*

Magnetars form a sub-population within the isolated neutron star zoo, occupying a unique parameter space in the famed period-period derivative diagram. Assuming magnetic dipole radiation, their inferred magnetic fields are on average two orders of magnitude larger than regular pulsars. This immense reservoir of magnetic energy fuels their bright persistent surface thermal, and magnetospheric non-thermal X-ray emission. It is also the driver of sub-second soft gamma-ray flashes, giant flares (brightest X-ray events detected, after the sun), and years-long outbursts during which extreme variability is observed; altered spectral and pulse shapes, glitching activity, strong timing noise, appearance of radio activity, among other attributes. Additionally, the large energy stock of magnetars is commonly invoked as a power source for other extreme transient phenomena, such as gamma-ray bursts, superluminous supernovae, ultra-luminous X-ray sources, and finally fast radio bursts (FRBs). Smoking-gun evidence for the latter occurred on 2020 April 28, when an FRB-like radio burst was simultaneously detected with an X-ray burst from the Galactic magnetar SGR 1935+2143. All these observational properties relate to the evolution of the magnetic-field in magnetars, the stress this imparts onto the star solid crust, and the way in which that impacts the exterior through magnetic field twists. In this talk, I will summarize the latest high energy observational results from a few Galactic magnetars, their relation to FRBs, and their strength in providing great insight into crustal physics, plasma physics, and radiative processes in high B-field regime.