On the suspected timing-offset-induced calibration error in the
  Wilkinson microwave anisotropy probe time-ordered data
  In the time-ordered data (TOD) files of the WMAP CMB observations, there is
an undocumented timing offset of -25.6 ms between the spacecraft attitude and
radio flux density timestamps. If the offset induced an error during
calibration of the raw TOD, then estimates of the WMAP CMB quadrupole might be
substantially in error. A timing error during calibration would not only induce
an artificial quadrupole-like signal in the mean sky map, it would also add
variance per pixel. This variance would be present in the calibrated TOD.
Low-resolution map-making as a function of timing offset should show a minimum
variance for the correct timing offset. Three years of the calibrated, filtered
WMAP 3-year TOD are compiled into sky maps at HEALPix resolution N_side=8,
individually for each of the K, Ka, Q, V and W band differencing assemblies
(DA's), as a function of timing offset. The median per map of the temperature
fluctuation variance per pixel is calculated and minimised against timing
offset. Minima are clearly present. The timing offsets that minimise the median
variance are -38 \pm 8 ms (K, Ka), -27 \pm 3 ms (Q), -43 \pm 8 ms (V), and -47
\pm 194 ms (W), i.e. an average of -30 \pm 3 ms, where the WMAP collaboration's
preferred offset is 0 \pm 1.7 ms. A non-parametric bootstrap analysis rejects
the latter at a significance of 99.999%. The hypothesis of a -25.6 ms offset,
suggested by Liu, Xiong & Li from the TOD file timing offset, is consistent
with these minima. It is difficult to avoid the conclusion that the WMAP
calibrated TOD and inferred maps are wrongly calibrated. CMB quadrupole
estimates (3/pi)C_2 based on the incorrectly calibrated TOD are overestimated
by roughly 64 \pm 6% (KQ85 mask) to 94 \pm 10% (KQ75 mask). Ideally, the WMAP
map-making pipelines should be redone starting from the uncalibrated TOD and
using the -25.6 ms timing offset correction.
