  Among Type Ia supernovae (SNe~Ia) exist a class of overluminous objects whose
ejecta mass is inferred to be larger than the canonical Chandrasekhar mass. We
present and discuss the UV/optical photometric light curves, colors, absolute
magnitudes, and spectra of three candidate Super-Chandrasekhar mass
SNe--2009dc, 2011aa, and 2012dn--observed with the Swift Ultraviolet/Optical
Telescope. The light curves are at the broad end for SNe Ia, with the light
curves of SN~2011aa being amongst the broadest ever observed. We find all three
to have very blue colors which may provide a means of excluding these
overluminous SNe from cosmological analysis, though there is some overlap with
the bluest of "normal" SNe Ia. All three are overluminous in their UV absolute
magnitudes compared to normal and broad SNe Ia, but SNe 2011aa and 2012dn are
not optically overluminous compared to normal SNe Ia. The integrated luminosity
curves of SNe 2011aa and 2012dn in the UVOT range (1600-6000 Angstroms) are
only half as bright as SN~2009dc, implying a smaller 56Ni yield. While not
enough to strongly affect the bolometric flux, the early time mid-UV flux makes
a significant contribution at early times. The strong spectral features in the
mid-UV spectra of SNe 2009dc and 2012dn suggest a higher temperature and lower
opacity to be the cause of the UV excess rather than a hot, smooth blackbody
from shock interaction. Further work is needed to determine the ejecta and 56Ni
masses of SNe 2011aa and 2012dn and fully explain their high UV luminosities.
