The Correlation of Spectral Lag Evolution with Prompt Optical Emission
  in GRB 080319B
  We report on observations of correlated behavior between the prompt gamma-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 CCF
methodology for determining the time-resolved spectral lag, are summarized as
follows. First, the evolution in the arrival offset of prompt gamma-ray photon
counts between Swift-BAT 15-25 keV and 50-100 keV energy bands (intrinsic
gamma-ray spectral lag) appears to be anti-correlated with the arrival offset
between prompt 15-350 keV gamma-rays and the optical emission observed by
TORTORA (extrinsic optical/gamma-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 power law fit to 15-150 keV Swift-BAT data at
~T+8+/-2 sec and ~T+48+/-1 sec. These spectral energy changes also coincide
with intervals whose time-resolved spectral lag values are consistent with
zero, at ~T+12+/-2 sec and ~T+50+/-2 sec. These results, which are robust
across heuristic permutations of Swift-BAT energy channels and varying temporal
bin resolution, have also been corroborated via independent analysis of
Konus-Wind data. This potential discovery may provide the first observational
evidence for an implicit connection between spectral lags and GRB emission
mechanisms in the context of canonical fireball phenomenology. Future work
includes exploring a subset of bursts with prompt optical emission to probe the
unique or ubiquitous nature of this result.
