We analyze first-year data of WMAP
to determine the significance of asymmetry in summed power between
arbitrarily defined opposite hemispheres.
We perform this analysis on maps that we create ourselves from
the time-ordered data, using software developed
independently of the WMAP
We find that over the multipole range
= [2,64], the significance of asymmetry is
value insensitive to both frequency and power spectrum.
We determine the smallest multipole ranges exhibiting
significant asymmetry, and find twelve, including
= [2,3] and [6,7],
for which the significance
Examination of the twelve ranges indicates both an improbable
association between the direction of maximum significance and the ecliptic
0.01), and that contours of least
significance follow great circles inclined relative to the ecliptic
at the largest scales. The great circle for
= [2,3] passes over
reported preferred axes and is insensitive to frequency,
while the great circle for
= [6,7] is aligned
with the ecliptic poles.
We examine how changing map-making parameters,
e.g., foreground masking, affects asymmetry.
Only one change appreciably reduces asymmetry:
asymmetry at large scales (
7) is rendered insignificant
if the magnitude of the WMAP
(368.11 km s
) is increased
2-6 km s
While confirmation of this result requires the recalibration of the
time-ordered data, such a systematic change would be
consistent with observations of frequency-independent asymmetry.
We conclude that the use of an incorrect dipole vector, in
a systematic or foreground process associated with the ecliptic,
may help to explain the observed power asymmetry.