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

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 similar to 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 similar to a few times 10(10)cm, and then slowed around the Alfven radius by an ultra-strong magnetic field, and in the meantime two major fragments of mass similar to 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.