UV-Optical Observation of Type Ia Supernova SN 2013dy in NGC 7250

Extensive and independent observations of Type Ia supernova (SN Ia) SN 2013dy are presented, including a larger set of $UBVRI$ photometry and optical spectra from a few days before the peak brightness to $\sim$ 200 days after explosion, and ultraviolet (UV) photometry spanning from $t \approx -10$ days to $t \approx\ +15$ days referring to the $B$ band maximum. The peak brightness (i.e., $M_{\rm B} = -19.65 \pm 0.40$ mag, $L_{\rm max} = [1.95 \pm 0.55] \times 10^{43}$ erg s$^{-1}$) and the mass of synthesised $^{56}$Ni (i.e., $M$($^{56}$Ni) = 0.90 $\pm$ 0.26 M$_{\odot}$) are calculated, and they conform to the expectation for a SN Ia with a slow decline rate (i.e., $Δm_{15}(B)$ = 0.90 $\pm$ 0.03 mag, Phillips 1993). However, the near infrared (NIR) brightness of this SN (i.e., $M_{\rm H} = -17.33 \pm 0.30$ mag) is at least 1.0 mag fainter than usual. Besides, spectroscopy classification reveals that SN 2013dy resides on the border of "core normal" and "shallow silicon" subclasses in the Branch et al. (2009) classification scheme, or on the border of the "normal velocity" SNe Ia and 91T/99aa-like events in the Wang et al. (2009a) system. These suggest that SN 2013dy is a slow-declining SN Ia located on the transitional region of nominal spectroscopic subclasses and might not be a typical normal sample of SNe Ia.

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