Can GRB 250702B be explained as the tidal disruption of a white dwarf by an intermediate mass black hole? Yes

TL;DR

GRB 250702B presents an unusual, repeating high-energy transient with multiwavelength counterparts that challenge conventional GRB progenitors. The authors propose a tidal disruption event in which a white dwarf on a bound orbit around an intermediate-mass black hole undergoes repeated stripping before final disruption, launching a wide, mildly relativistic jet; MeV gamma-rays arise from upscattering of shock-generated seed photons by the jet, while X-ray, NIR, and radio emission are explained by fallback accretion, thermal emission, and external shocks. A semi-analytical fallback model is fitted to the X-ray light curve to constrain the system’s masses and jet properties, yielding results consistent with the measured redshift $z=1.036$ and $E_{ m iso}\sim 2\times10^{54}$ erg. Formation via Hills capture and rate estimates imply a rare but plausible channel for WD-IMBH TDEs, aligning with the event’s uniqueness. Overall, this WD-IMBH TDE framework provides a coherent explanation for GRB 250702B and motivates searches for similar repeating high-energy transients.

Abstract

GRB 250702B is a unique astrophysical transient characterised by its nature as a repeating gamma-ray trigger. Its properties include possible periodicity in its gamma-ray light curve, an X-ray counterpart that rose prior to the gamma-ray outbursts and faded quickly, and radio and infrared counterparts. These features are difficult to reconcile with most models of high energy transients but we show that they are compatible with a white dwarf bound to an intermediate mass black hole that is tidally stripped over multiple pericentre passages before being fully disrupted. Accretion onto the black hole powers a mildly relativistic jet that produces the X-rays through internal processes and the infrared and radio counterparts through thermal emission and external shocks respectively but is unable to produce the gamma-ray emission on its own. We propose that chaotic debris streams from the multiple stripping episodes can collide with a period roughly the same as the orbital period of the star. These shocks produce hard X-ray photons that are upscattered by the jet to produce the observed MeV gamma-ray emission. Future analysis of the jet properties will allow us to place firmer constraints on our model.

Figures (2)

• Figure 1: The long term X-ray light curve of GRB 250702B compared to all 177 1-$\sigma$ traces from our MCMC fit using a WD-IMBH model (blue solid lines). The vertical grey lines mark the times of the Fermi triggers. Note the first plotted WXT point is excluded from our fitting.
• Figure 2: Top: the differential mass per unit specific orbital energy distribution of a disrupted WD derived using the frozen-in approximation (black), numerical simulations Cufari22a and our semi-analytical approximation (blue). An eccentricity of $e=1$ is assumed here. Bottom: the ratio between our semi-analytical approximation and the numerical result of Cufari22a.