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Early observations of Type Ia supernovae (SNe$,$Ia) provide essential clues for understanding the progenitor system that gave rise to the terminal thermonuclear explosion. We present exquisite observations of SN$,$2019yvq, the second observed SN$,$Ia, after iPTF$,$14atg, to display an early flash of emission in the ultraviolet (UV) and optical. Our analysis finds that SN$,$2019yvq was unusual, even when ignoring the initial flash, in that it was moderately underluminous for an SN$,$Ia ($M_g approx -18.5,$mag at peak) yet featured very high absorption velocities ($v approx 15,000,mathrm{km,s}^{-1}$ for Si II $lambda$6355 at peak). We find that many of the observational features of SN$,$2019yvq, aside from the flash, can be explained if the explosive yield of radioactive $^{56}mathrm{Ni}$ is relatively low (we measure $M_{^{56}mathrm{Ni}} = 0.31 pm 0.05,M_odot$) and it and other iron-group elements are concentrated in the innermost layers of the ejecta. To explain both the UV/optical flash and peak properties of SN$,$2019yvq we consider four different models: interaction between the SN ejecta and a nondegenerate companion, extended clumps of $^{56}mathrm{Ni}$ in the outer ejecta, a double-detonation explosion, and the violent merger of two white dwarfs. Each of these models has shortcomings when compared to the observations; it is clear additional tuning is required to better match SN$,$2019yvq. In closing, we predict that the nebular spectra of SN$,$2019yvq will feature either H or He emission, if the ejecta collided with a companion, strong [Ca II] emission, if it was a double detonation, or narrow [O I] emission, if it was due to a violent merger.
We present photometric and spectroscopic observations of the nearby Type Ia SN 2019yvq, from its discovery $sim$1 day after explosion to $sim$100 days after its peak brightness. This SN exhibits several unusual features, most notably an extremely bri
PTF09dav is a peculiar subluminous type Ia supernova (SN) discovered by the Palomar Transient Factory (PTF). Spectroscopically, it appears superficially similar to the class of subluminous SN1991bg-like SNe, but it has several unusual features which
We present ultraviolet (UV) and optical photometry and spectra of the 1999aa-like supernova (SN) iPTF14bdn. The UV data were observed using the Swift Ultraviolet/Optical Telescope (UVOT) and constitute the first UV spectral series of a 1999aa-like SN
We present photospheric-phase observations of LSQ12gdj, a slowly-declining, UV-bright Type Ia supernova. Classified well before maximum light, LSQ12gdj has extinction-corrected absolute magnitude $M_B = -19.8$, and pre-maximum spectroscopic evolution
We present ultraviolet (UV) spectroscopy and photometry of four Type Ia supernovae (SNe 2004dt, 2004ef, 2005M, and 2005cf) obtained with the UV prism of the Advanced Camera for Surveys on the Hubble Space Telescope. This dataset provides unique spect