Arrival Times of Multi-TeV Photons from GRB 221009A and the Dispersion Scale

GRB 221009A, the brightest gamma-ray burst yet recorded, at redshift 0.151, was detected by LHAASO at energies extending to about 18 TeV — photons that should have been heavily attenuated by background light, arriving from a burst whose low-energy onset is known to the second. Charging the entire roughly 2000-second TeV detection window to propagation bounds a linear dispersion scale at 6.441e+17 GeV and a quadratic scale at 1.368e+11 GeV; charging only the sharp early structure of the TeV light curve, an adopted 250 seconds, raises those figures to 5.153e+18 GeV and 3.870e+11 GeV. The quadratic figure is the notable one: TeV photons over a two-billion-year lookback give the quadratic term nowhere to hide at scales where GeV bursts are blind to it. The framework examined here predicts no propagation delay at any energy; the burst's TeV arrival pattern is consistent with that prediction. Computed from published data; not a new measurement.