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

Abstract

The longest detected gamma-ray burst, GRB250702B, exhibited seven hours of prompt $\gamma$-ray emission, preceded by a soft X-ray precursor ($\sim 1$ day earlier) and followed by a weeks-long fading X-ray tail. Lacking an established progenitor for all three phases, we propose that this ultra-long GRB (ULGRB) is powered by a jetted micro-tidal disruption event (micro-TDE), in which a spinning stellar-mass black hole (BH) disrupts a Sun-like star and launches a relativistic jet via the Blandford-Znajek mechanism. Micro-TDE debris disks have hours-to-days viscous timescales, naturally explaining ULGRB durations. Using 3D hydrodynamic AREPO simulations of a $1M_{\odot }$ star disrupted by a $10M_{\odot }$ BH, we show that within $\sim 1$ day the debris forms a quasi-steady envelope with a low-density polar funnel ($\rho \propto r^{-2}$, half-opening angle $\approx 15^{\circ }$). Applying an analytic jet-stability framework to these profiles, we find that the $r^{-2}$ funnel keeps the jet below the kink-instability threshold, enabling stable propagation and breakout for jet powers, $L_{\mathrm{jet}}\gtrsim 10^{47}$ erg s${}^{-1}$. We attribute the X-ray precursor to pre-disk stream-fed accretion; the prompt GRB to a tightly beamed jet (${\theta }_{\mathrm{b}}\lesssim 1^{\circ }$, $L_{\gamma ,\mathrm{iso}}\sim 10^{51}$ erg s${}^{-1}$) escaping the funnel, launched by a rapidly spinning BH ($a_{\bullet }\sim 0.9$); and the weeks-long X-ray decline to disk-wind mass loss ($L_{\mathrm{jet}}\propto t^{-2}$) combined with jet widening (${\theta }_{\mathrm{b}}\propto t$, initially steepening the decay to $L_{\mathrm{X},\mathrm{iso}}\propto L_{\mathrm{jet}}/{\theta }_{\mathrm{b}}^2\propto t^{-4}$). Our model reproduces the multi-phase evolution of GRB250702B and establishes jetted micro-TDEs as a physically motivated ULGRB engine.

16 pages, 6 figures, submitted to ApJL