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We present photospheric-phase observations of LSQ12gdj, a slowly-declining,UV-bright Type Ia supernova. Classified well before maximum light, LSQ12gdj hasextinction-corrected absolute magnitude $M_B = -19.8$, and pre-maximumspectroscopic evolution similar to SN 1991T and the super-Chandrasekhar-mass SN2007if. We use ultraviolet photometry from Swift, ground-based opticalphotometry, and corrections from a near-infrared photometric template toconstruct the bolometric (1600-23800 \AA) light curve out to 45 days past$B$-band maximum light. We estimate that LSQ12gdj produced $0.96 \pm 0.07$$M_\odot$ of $^{56}$Ni, with an ejected mass near or slightly above theChandrasekhar mass. As much as 27% of the flux at the earliest observed phases,and 17% at maximum light, is emitted bluewards of 3300 \AA. The absence ofexcess luminosity at late times, the cutoff of the spectral energy distributionbluewards of 3000 \AA, and the absence of narrow line emission and strong Na ID absorption all argue against a significant contribution from ongoing shockinteraction. However, up to 10% of LSQ12gdj's luminosity near maximum lightcould be produced by the release of trapped radiation, including kinetic energythermalized during a brief interaction with a compact, hydrogen-poor envelope(radius $< 10^{13}$ cm) shortly after explosion; such an envelope arisesgenerically in double-degenerate merger scenarios.

Early ultraviolet emission in the Type Ia supernova LSQ12gdj: No evidence for ongoing shock interaction