A freely precessing magnetar following an X-ray outburst.

Magnetars-highly magnetized neutron stars-are thought to be the most likely progenitors for fast radio bursts (FRBs). Freely precessing magnetars are further invoked to explain the repeating FRBs. We report here on new high-cadence radio observations of the magnetar XTE J1810-197 recorded shortly after an X-ray outburst. We interpret the polarization variations of the magnetar radio emission as evidence for the magnetar undergoing free precession following the outburst while its magnetosphere slowly untwists. The observations of precession being damped on a timescale of months argue against the scenario of freely precessing magnetars as the origin of repeating FRBs. Using free-precession models based on relaxing ellipticity with a decay of the wobble angle, we find the magnetar ellipticity to be in good agreement with theoretical predictions from nuclear physics. Our precise measurement of the magnetar's geometry can also further help in refining the modelling of X-ray light curves and constrain the star's compactness.

Discovery of a radio emitting neutron star with an ultra-long spin period of 76 seconds.

The radio-emitting neutron star population encompasses objects with spin periods ranging from milliseconds to tens of seconds. As they age and spin more slowly, their radio emission is expected to cease. We present the discovery of an ultra-long period radio-emitting neutron star, PSR J0901-4046, with spin properties distinct from the known spin and magnetic-decay powered neutron stars. With a spin-period of 75.88 s, a characteristic age of 5.3 Myr, and a narrow pulse duty-cycle, it is uncertain how radio emission is generated and challenges our current understanding of how these systems evolve. The radio emission has unique spectro-temporal properties such as quasi-periodicity and partial nulling that provide important clues to the emission mechanism. Detecting similar sources is observationally challenging, which implies a larger undetected population. Our discovery establishes the existence of ultra-long period neutron stars, suggesting a possible connection to the evolution of highly magnetized neutron stars, ultra-long period magnetars, and fast radio bursts.

Unifying repeating fast radio bursts.

Mysterious high-energy radio bursts are found to share certain characteristics.