A Precessing, Magnetically Dominated, Structured Jet Powering the Hour-scale Quasiperiodic GRB 250702B

Abstract

GRB 250702B shows ultra-long, episodic prompt activity (three hard gamma-ray episodes over ~ 3.2 h with quasi-regular spacing P~ 2825 s preceded by a soft X-ray flare about one day earlier. We interpret these phenomena with a unified scenario in which a stellar-mass black hole accretes from a massive, misaligned debris disk and launches a magnetically dominated, precessing, structured (spine-sheath) jet. The engine "clock" arises from Lense-Thirring precession of the outer annulus of a geometrically thick inner torus at r ~ 250-300 rg, while the hard spectra reflect magnetic-reconnection dissipation in the spine. A slightly off-axis viewing geometry resolves the apparent opening-angle tension without invoking late energy injection. "Missing" pulses in the second/third cycles occur naturally when low-amplitude nutation causes the beaming cone to miss the line of sight. The model yields concrete, falsifiable predictions, providing a self-consistent explanation of GRB 250702B's radiative and outflow anomalies.