A Magnetar-asteroid Impact Model for FRB 200428 Associated with an X-Ray Burst from SGR 1935+2154

Abstract

Very recently, an extremely bright fast radio burst (FRB) 200428 with two submillisecond pulses was discovered coming from the direction of the Galactic magnetar SGR 1935+2154, and an X-ray burst (XRB) counterpart was detected simultaneously. These observations favor magnetar-based interior-driven models. In this Letter, we propose a different model for FRB 200428 associated with an XRB from SGR 1935+2154 in which a magnetar with high proper velocity encounters an asteroid of mass ∼10 20 g. This infalling asteroid in the stellar gravitational field is first possibly disrupted tidally into a great number of fragments at a radius of ∼a few times 10 10 cm, and then slowed around the Alfvén radius by an ultra-strong magnetic field, and in the meantime two major fragments of mass ∼10 17 g that cross magnetic field lines produce two pulses of FRB 200428. The whole asteroid is eventually accreted onto the poles along magnetic field lines, impacting the stellar surface, creating a photon-e ±  pair fireball trapped initially in the stellar magnetosphere, and further leading to an XRB. We show that this gravitationally powered model can interpret all of the observed features self-consistently.