A Correlation of Spectral Lag Evolution with Prompt Optical Emission in GRBs?

We report on observations of correlated behavior between the prompt γ-ray and optical emission from GRB 080319B, which (i) strongly suggest that they occurred within the same astrophysical source region and (ii) indicate that their respective radiation mechanisms were most likely dynamically coupled. Our preliminary results, based upon a new cross-correlation function (CCF) methodology for determining the time-resolved spectral lag, are summarized as follows. First, the evolution in the arrival offset of prompt γ-ray photon counts between Swift-BAT 15-25 keV and 50-100 keV energy bands (intrinsic γ-ray spectral lag) appears to be anti-correlated with the arrival offset between prompt 15-350 keV γ-rays and the optical emission observed by TORTORA (extrinsic optical/γ-ray spectral lag), thus effectively partitioning the burst into two main episodes at ∼ T +28±2 sec. Second, prompt optical emission is nested within intervals of (a) trivial intrinsic γ-ray spectral lag (∼ T +12±2 and ∼ T +50±2 sec) with (b) discontinuities in the hard to soft evolution of the photon index for a power law fit to 15-150 keV Swift-BAT data (∼ T +8±2 and ∼ T +48±1 sec), both of which coincide with the rise (∼ T +10±1 sec) and decline (∼ T +50±1 sec) of prompt optical emission. This potential discovery, robust across heuristic permutations of BAT energy channels and varying temporal bin resolution, provides the first observational evidence for an implicit connection between spectral lag and the dynamics of shocks in the context of canonical fireball phenomenology.