  Using extensive HST imaging, combined with Chandra X-ray and Parkes radio
data, we have detected the optical binary companion to a second millisecond
pulsar (MSP) in the globular cluster 47 Tucanae. This faint (V=22.3) blue
(V-I=0.7) star shows a large amplitude (60-70%) sinusoidal variation in both V
and I. The period (3.19066 hr) and phase of the variation match those of the
MSP 47 Tuc W (which does not have an accurate radio timing position) to within
0.5 seconds and 1.2 minutes respectively, well within the ~1sigma errors. The
phase dependence of the intensity and color implies that heating of a tidally
locked companion causes the observed variations. The eclipsing nature of this
MSP in the radio, combined with the relatively large companion mass (> 0.13
solar masses) and the companion's position in the color-magnitude diagram,
suggest that the companion is a main sequence star, a rare circumstance for an
MSP companion. This system is likely to have had a complex evolution and
represents an interesting case study in MSP irradiation of a close companion.
We present evidence for another optical variable with similar properties to the
companion of 47 Tuc W. This variable may also be an MSP companion, although no
radio counterpart has yet been detected.
