  Two decades after the discovery of 51 Peg b, the formation processes and
atmospheres of short-period gas giants remain poorly understood. Observations
of eccentric systems provide key insights on those topics as they can
illuminate how a planet's atmosphere responds to changes in incident flux. We
report here the analysis of multi-day multi-channel photometry of the eccentric
(e~ 0.93) hot Jupiter HD 80606 b obtained with the Spitzer Space Telescope. The
planet's extreme eccentricity combined with the long coverage and exquisite
precision of new periastron-passage observations allow us to break the
degeneracy between the radiative and dynamical timescales of HD 80606 b's
atmosphere and constrain its global thermal response. Our analysis reveals that
the atmospheric layers probed heat rapidly (~4 hr radiative timescale) from
$\lt$500 to 1400 K as they absorb ~ 20% of the incoming stellar flux during the
periastron passage, while the planet's rotation period is 93$\pm_{35}^{85}$ hr,
which exceeds the predicted pseudo-synchronous period (40 hr).
