Repeating fast radio bursts caused by small bodies orbiting a pulsar or a magnetar

¹ LUTH, Observatoire de Paris, PSL Research University, CNRS, Université de Paris, 5 Place Jules Janssen, 92190 Meudon, France
e-mail: fabrice.mottez@obspm.fr
² LESIA, Observatoire de Paris, PSL Research University, CNRS, Université de Paris, Sorbonne Université, 5 Place Jules Janssen, 92190 Meudon, France
³ Jodrell Bank Centre for Astrophysics, Department of Physics and Astronomy, The University of Manchester, Manchester M19 9PL, UK

Received: 16 February 2020
Accepted: 1 October 2020

Abstract

Context. Asteroids orbiting into the highly magnetized and highly relativistic wind of a pulsar offer a favorable configuration for repeating fast radio bursts (FRB). The body in direct contact with the wind develops a trail formed of a stationary Alfvén wave, called an Alfvén wing. When an element of wind crosses the Alfvén wing, it sees a rotation of the ambient magnetic field that can cause radio-wave instabilities. In the observer’s reference frame, the waves are collimated in a very narrow range of directions, and they have an extremely high intensity. A previous work, published in 2014, showed that planets orbiting a pulsar can cause FRBs when they pass in our line of sight. We predicted periodic FRBs. Since then, random FRB repeaters have been discovered.

Aims. We present an upgrade of this theory with which repeaters can be explained by the interaction of smaller bodies with a pulsar wind.

Methods. Considering the properties of relativistic Alfvén wings attached to a body in the pulsar wind, and taking thermal consideration into account, we conducted a parametric study.

Results. We find that FRBs, including the Lorimer burst (30 Jy), can be explained by small-size pulsar companions (1 to 10 km) between 0.03 and 1 AU from a highly magnetized millisecond pulsar. Some parameter sets are also compatible with a magnetar. Our model is compatible with the high rotation measure of FRB 121102. The bunched timing of the FRBs is the consequence of a moderate wind turbulence. An asteroid belt composed of fewer than 200 bodies would suffice for the FRB occurrence rate measured with FRB 121102.

Conclusions. After this upgrade, this model is compatible with the properties discovered since its first publication in 2014, when repeating FRBs were still unknown. It is based on standard physics and on common astrophysical objects that can be found in any type of galaxy. It requires 10¹⁰ times less power than (common) isotropic-emission FRB models.