Black-to-white hole transitions could produce fast, isotropic MeV-GeV transients via Weibel-mediated external shocks
The preprint calculates non-thermal signatures of black-to-white hole explosions interacting with the ISM, forecasting brief, isotropic afterglows distinguishable from short GRBs. Evidence rests on analytic one-zone modeling with illustrative parameters rather than full simulations. Key uncertainties include the assumed R_k fraction and neglect of reverse-shock or lateral structure contributions.
The study parametrizes kinetic energy as R_k times prompt gamma-ray energy and applies one-zone Thomson-regime radiation to a forward shock with Weibel-generated magnetic fields. Electrons remain slow-cooling for p=2.5, placing the spectral peak at the cooling frequency that softens over seconds while self-absorption and gamma-gamma opacity shape the low- and high-energy ends. Detectability estimates show 1 keV photon counts can exceed thresholds for optimistic microphysical parameters and ISM densities around 1 cm^-3. This setup yields roughly isotropic events without achromatic jet breaks, differing from classical GRB afterglows by orders of magnitude in duration at comparable energy and Lorentz factor. The analysis connects to prior photospheric prompt models and highlights sensitivity to R_k, epsilon_e, epsilon_B, and xi_e, yet remains limited by forward-shock-only dynamics and order-of-magnitude accuracy. Future multi-messenger searches with wide-field MeV instruments could test the scenario if rates reach 10^-3 Gpc^-3 yr^-1. Distinguishing features include a hard prompt flash followed by a fast faint tail, potentially overlapping with rare magnetar flares but lacking their periodicity.
Fermi-GBM or future MeV telescopes: First candidate isotropic fast transient with MeV peak and sub-10 s duration without jet break detected within 3 years if event rate exceeds 0.001 Gpc^-3 yr^-1
Sources (2)
- [1]Primary Source(https://arxiv.org/abs/2608.12380)
- [2]Supporting Source(https://arxiv.org/abs/astro-ph/9909271)