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From the set of nearly 500 spectroscopically confirmed type~Ia supernovae andaround 10,000 unconfirmed candidates from SDSS-II, we select a subset of 108confirmed SNe Ia with well-observed early-time light curves to search forsignatures from shock interaction of the supernova with a companion star. Noevidence for shock emission is seen; however, the cadence and photometric noisecould hide a weak shock signal. We simulate shocked light curves using SN Iatemplates and a simple, Gaussian shock model to emulate the noise properties ofthe SDSS-II sample and estimate the detectability of the shock interactionsignal as a function of shock amplitude, shock width, and shock fraction. Wefind no direct evidence for shock interaction in the rest-frame $B$-band, butplace an upper limit on the shock amplitude at 9% of supernova peak flux ($M_B> -16.6$ mag). If the single degenerate channel dominates type~Ia progenitors,this result constrains the companion stars to be less than about 6 $M_{\odot}$on the main sequence, and strongly disfavors red giant companions.

Single or Double Degenerate Progenitors? Searching for Shock Emission in the SDSS-II Type Ia Supernovae