Explaining the X-ray Precursor, Ultra-long Prompt Emission, and Week-long Decay of GRB250702B with a Jetted Micro-TDE

GRB250702B is the longest detected gamma-ray burst, showing seven hours of prompt gamma-ray emission, preceded by a soft X-ray precursor about one day earlier and followed by a weeks-long fading X-ray tail. No existing progenitor model could explain all three phases together, motivating the search for a new physical engine.

The authors propose that this ultra-long GRB (ULGRB) is powered by a jetted micro-tidal disruption event: a spinning stellar-mass black hole (BH) disrupts a Sun-like star and launches a relativistic jet via the Blandford-Znajek mechanism. The hours-to-days viscous timescales of micro-TDE debris disks naturally account for the extended ULGRB duration. To test this, they ran 3D hydrodynamic AREPO simulations of a 1 solar-mass star disrupted by a 10 solar-mass BH. Within about a day, the debris forms a quasi-steady envelope with a low-density polar funnel of density profile rho ~ r^-2 and half-opening angle ~15 degrees.

Applying an analytic jet-stability framework to these simulated profiles, they find the r^-2 funnel keeps the jet below the kink-instability threshold, enabling stable propagation and breakout for jet powers L_jet >= 10^47 erg/s. The model attributes the X-ray precursor to stream-fed accretion before the disk forms; the prompt GRB to a tightly beamed jet (opening angle theta_b <= 1 deg, isotropic gamma luminosity ~10^51 erg/s) launched by a rapidly spinning BH (spin a ~ 0.9) that escapes through the funnel; and the weeks-long X-ray decline to disk-wind mass loss (L_jet ~ t^-2) combined with jet widening (theta_b ~ t), which initially steepens the decay to L_X,iso ~ L_jet/theta_b^2 ~ t^-4.

This scenario reproduces the multi-phase evolution of GRB250702B and establishes jetted micro-TDEs as a physically motivated engine for ultra-long gamma-ray bursts.