The Correlation of Spectral Lag Evolution with Prompt Optical Emission in GRB 080319B

We report on observations of correlated behavior between the prompt γ‐ray and optical emission from GRB 080319B, which confirm that (i) they occurred within the same astrophysical source region and (ii) their respective radiation mechanisms were dynamically coupled. Our 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, the rise and decline of prompt optical emission at ∼T+10±1 sec and ∼T+50±1 sec, respectively, both coincide with discontinuities in the hard to soft evolution of the photon index for a...