We report the detection of 24 micron variations from the planet-hosting
upsilon Andromedae system consistent with the orbital periodicity of the
system's innermost planet, upsilon And b. We find a peak-to-valley phase curve
amplitude of 0.00130 times the mean system flux. Using a simple model with two
hemispheres of constant surface brightness and assuming a planetary radius of
1.3 Jupiter radii gives a planetary temperature contrast of >900 K and an
orbital inclination of >28 degrees. We further report the largest phase offset
yet observed for an extrasolar planet: the flux maximum occurs ~80 degrees
before phase 0.5. Such a large phase offset is difficult to reconcile with most
current atmospheric circulation models. We improve on earlier observations of
this system in several important ways: (1) observations of a flux calibrator
star demonstrate the MIPS detector is stable to 10^-4 on long timescales, (2)
we note that the background light varies systematically due to spacecraft
operations, precluding use of this background as a flux calibrator (stellar
flux measured above the background is not similarly affected), and (3) we
calibrate for flux variability correlated with motion of the star on the MIPS
detector. A reanalysis of our earlier observations of this system is consistent
with our new result.Comment: Submitted to ApJ. 15 pages, 6 figures, 4 table