On the Origin of Radio Emission from Magnetars

TL;DR

This paper explains the radio emission from magnetars using the partially screened gap model, linking their magnetic, thermal, and rotational properties to their radio visibility.

Contribution

It introduces a model that predicts magnetar radio emission based on surface temperature, magnetic field structure, and rotational parameters, unifying magnetar and pulsar radio emission mechanisms.

Findings

Radio emission requires the polar cap temperature to be at the critical value.

Magnetars must have sufficient rotational energy to heat the polar cap.

Magnetic field alterations increase radio beam visibility.

Abstract

Magnetars are the most magnetized objects in the known universe. Powered by the magnetic energy, and not by the rotational energy as in the case of radio pulsars, they have long been regarded as a completely different class of neutron stars. The discovery of pulsed radio emission from a few magnetars weakened the idea of a clean separation between magnetars and normal pulsars. We use the partially screened gap (PSG) model to explain radio emission of magnetars. The PSG model requires that the temperature of the polar cap is equal to the so-called critical value, i.e., the temperature at which the thermal ions outflowing from the stellar surface screen the acceleration gap. We show that a magnetar has to fulfill the temperature, power, and visibility conditions in order to emit radio waves. First, in order to form PSG, the residual temperature of the surface has to be lower than the critical value. Second, since the radio emission is powered by the rotational energy, it has to be high enough to enable heating of the polar cap by backstreaming particles to the critical temperature. Finally, the structure of the magnetic field has to be altered by magnetospheric currents in order to widen a radio beam and increase the probability of detection. Our approach allows us to predict whether a magnetar can emit radio waves using only its rotational period, period derivative, and surface temperature in the quiescent mode.