A milli-Tidal Disruption Event Model for GRB 250702B: Main Sequence Star Disrupted by an IMBH

GRB 250702B is the longest GRB recorded so far, with multiple gamma-ray emission episodes spread over a duration exceeding 25 ks and a weaker soft X-ray pre-peak ~1 day gradually rising emission. It is offset from its host galaxy center by ~5.7 kpc, and displays a long-lived afterglow emission in radio to X-ray. Its true nature is unclear, with the two leading candidate classes of objects being a peculiar type of ultra-long GRB and a tidal disruption event (TDE) by an intermediate mass black hole (IMBH). Here, we consider the latter, mTDE origin. We model the afterglow data, finding a stratified external density profile ∝r−k with k = 1.60 ± 0.17, consistent with Bondi accretion of the interstellar medium (of initial number density nISM = n0 cm−3 and sound speed cs = cs, 6106 cm s−1) for which n(r) ≈ nISM(r/RB)−3/2 within the Bondi radius RB. Moreover, we use the implied density normalization to infer the IMBH mass within this model, finding M_• ≈ (6.55+3.51-2.29)× 10³\, n₀-2/3\, cs,6²(1+M²)\, M_ where M≡ vBH/cₛ is the IMBH’s Mach number relative to the ISM. Together with an upper limit on M_• <c³/GtMV1+z 5× 10⁴\, M_ from the source-frame minimum variability time tMV,src\!=\!tMV1+z\!≈ \!0.5\,s this implies vBH 28\, n₀1/3\, km\, s⁻¹. We show that a mTDE of a main-sequence star (but not of a white dwarf) can explain the duration and energetics of GRB 250702B. The gradual rise to the peak may be caused by gradual circularization and accretion disk buildup, leading to an increase in the jet’s power and Lorentz factor.