Fast radio bursts are millisecond-long flashes of radio waves that originate primarily from outside our galaxy. Although their frequency is high, about 5,000 per day across the entire sky, they were first detected only in 2007. There are now about a thousand of them, mainly since the advent of CHIME, a Canadian radio telescope. These signals have a wide range of properties that have never been observed before and are difficult to interpret. Although several distinct origins are possible, there is evidence that some of these bursts are associated with magnetars, neutron stars with particularly intense magnetic fields.
When the crust of a magnetar trembles, considerable energy is transferred to the magnetosphere in the form of magnetic waves. Monster shocks belong to a class of shocks formed by the stiffening of waves propagating perpendicular to the magnetic field lines ; these are called fast magnetosonic waves. They are called “monsters” because of their immense power, a term coined by a Columbia University professor who first studied their large-scale dynamics in 2023. While at the macroscopic scale, we understand the stiffening of the wave and its dissipation in a shock, the description and radiative signature of this highly nonlinear dissipative phenomenon at microscopic scales remained unknown.
The proposed scenario was identified using kinetic numerical simulations of plasmas composed of electron-positron pairs that, for the first time, reveal the detailed multiscale structure of these monster shocks. By resolving its dynamics at small scales, the researchers demonstrated the self-consistent production of a signal whose energy represents 0.1% of the total energy dissipated by the shock. This promising mechanism for the interpretation of fast radio bursts presents a characteristic spectral shape in the radio domain for physical conditions anticipated within magnetars. The two researchers also corroborated this numerical study with a theoretical model of the dynamics of these shocks. Overall, the study offers interesting perspectives on the dissipation and signature of magnetic pulses in highly magnetized environments.
