Using large-scale particle-in-cell simulations, Amir Levinson and Arno Vanthieghem studied how a fast magnetosonic wave, produced near a magnetar, propagates through the declining magnetic field of the inner magnetosphere, steepens, and eventually breaks. The wave forms a ‘monster shock’ when the electric and magnetic fields reach comparable strengths, B² − E² → 0. After forming the shock, the wave dissipates approximately half of its initial energy.

For the first time, the simulations show that the shock generates a high-frequency precursor wave carrying roughly ~10⁻³ of the dissipated energy. Its spectrum features sharp harmonic peaks in the GHz band, consistent with the frequencies observed in fast radio bursts. Under magnetar conditions, the precursor from the monster shock is strong enough to account for the fast radio bursts observed from the galactic magnetar SGR 1935+2154.

These results provide a self-consistent mechanism linking magnetic wave breaking in magnetars to observable radio transients and open new directions for understanding fast radio bursts from magnetars.

This work, led by postdoctoral fellow Koushik Chatterjee in collaboration with Alexander Philippov (UMd), Andrei Beloborodov (Columbia), Bart Ripperda (CITA), and other collaborators, presents the first relativistic magnetohydrodynamic simulation of a surface shear–driven eruption in a magnetar’s magnetosphere. The study shows how gradual crustal deformation can trigger giant flares with energies exceeding 10⁴⁴ erg.

The simulations show that once the magnetic twist exceeds a critical threshold, the magnetosphere inflates and reconnection occurs in its tail. A large fraction of the dipole energy is released in a giant plasmoid, whose trailing hot plasma may produce the main spike of the gamma-ray flare. Hot plasma trapped in the closed magnetosphere forms a fireball that powers the extended X-ray tail. The ejecta also launches a strong compressive wave—a fast magnetosonic pulse—carrying enough energy to potentially produce fast radio bursts.

Although the simulated flare timescale is shorter than observed, uncertainties in reconnection physics—especially in the highly radiative environment near the magnetar—may substantially influence both the reconnection rate and the flare duration, highlighting an important challenge for future studies.

This study proposes a plasma mechanism to explain the unusual radio emission from quiescent magnetars. Led by Shuzhe Zeng, a graduate student at the University of Maryland, together with Alexander Philippov (Maryland) and Andrei Beloborodov (Columbia), the team shows that the emission originates from a closed, twisted bundle of magnetic field lines near the magnetic pole, stretching roughly 15–50 stellar radii. In this region, an electron–positron plasma must carry electric current while also experiencing strong drag from the magnetar’s intense X-ray radiation. This drag locks the plasma into a state that becomes unstable to a two-stream plasma instability. Kinetic simulations using a novel computational code show that the turbulence from this instability generates electromagnetic waves that can escape as radio emission.

The model naturally explains several observed features of magnetar radio signals, including their brightness (~10³⁰ erg/s), wide pulses, strong linear polarization, delayed appearance following X-ray outbursts, and a broad spectrum from GHz frequencies up to nearly 100 GHz. Researchers are currently investigating the plasma mechanisms responsible for producing superluminal waves and their spectral properties, with the goal of comparing them to magnetar observations.