Magnetic Cannonball Model for Gamma‐Ray Bursts

Abstract

We propose a new magnetic-driven mechanism for gamma-ray bursts. The collapse of a magnetosphere onto a black hole can generate a strong outward Poynting flux that drives a baryon-free fireball called the magnetic cannonball. The relativistic outflow of the cannonball interacts with interstellar matter and forms a shock with the help of its magnetic field. The magnetic field of 10⁴ G at the shock can induce synchrotron radiation with peaks observed at 10² keV. This magnetic field in the cannonball can also confine high-energy protons (γ_p > 30), which are required for delayed high-energy photons (>25 GeV), which were observed following a burst on 1994 February 17. Accretion-induced collapse of a white dwarf with a magnetic field of greater than 10⁹ G, merger of a close binary, and failed Type Ib supernovae are possible creation scenarios, even without the rotation of the central object. This mechanism induces another burst event at the final phase of gravitational collapse even after a neutrino-driven fireball induces a burst event. In this scenario, the bursts consist of a primary neutrino-driven fireball and a secondary magnetic cannonball. This suggests that the magnetic cannonball works in some populations of gamma-ray bursts and in delayed or multiple burst events. The final remnant in the model should be a black hole. This implies that gamma-ray bursts cannot have an optical counterpart like a single star if they do not have a companion in a binary.