If Type Ia supernovae (SNe~Ia) result from a white dwarf being ignited by
Roche lobe overflow from a nondegenerate companion, then as the supernova
explosion runs into the companion star its ejecta will be shocked, causing an
early blue excess in the lightcurve. A handful of these excesses have been
found in single-object studies, but inferences about the population of SNe~Ia
as a whole have been limited because of the rarity of multiwavelength followup
within days of explosion. Here we present a three-year investigation yielding
an unbiased sample of nine nearby (z<0.01) SNe~Ia with exemplary early data.
The data are truly multiwavelength, covering UBVgri and Swift bandpasses, and
also early, with an average first epoch 16.0 days before maximum light. Of the
nine objects, three show early blue excesses. We do not find enough statistical
evidence to reject the null hypothesis that SNe~Ia predominantly arise from
Roche-lobe-overflowing single-degenerate systems (p=0.94). When looking at
the objects' colors, we find the objects are almost uniformly near-UV-blue, in
contrast to earlier literature samples which found that only a third of SNe~Ia
are near-UV-blue, and we find a seemingly continuous range of B−V colors in
the days after explosion, again in contrast with earlier claims in the
literature. This study highlights the importance of early, truly
multiwavelength, high-cadence data in determining the progenitor systems of
SNe~Ia and in revealing their diverse early behavior.Comment: 28 pages, 10 figure