500 days of SN 2013dy: spectra and photometry from the ultraviolet to the infrared

SN 2013dy is a Type Ia supernova (SN Ia) for which we have compiled an extraordinary data set spanning from 0.1 to ∼ 500 d after explosion. We present 10 epochs of ultraviolet (UV) through near-infrared (NIR) spectra with <it>Hubble Space Telescope</it>/Space Telescope Imaging Spectrograph, 47 epochs of optical spectra (15 of them having high resolution), and more than 500 photometric observations in the <it>BVrRiIZYJH</it> bands. SN 2013dy has a broad and slowly declining light curve (Δ<it>m</it><inf>15</inf>(<it>B</it>) = 0.92 mag), shallow <f>$\\mathrm{Si}\\,\\small {II}\\,\\lambda 6355$</f> absorption, and a low velocity gradient. We detect strong C <scp>ii</scp> in our earliest spectra, probing unburned progenitor material in the outermost layers of the SN ejecta, but this feature fades within a few days. The UV continuum of SN 2013dy, which is strongly affected by the metal abundance of the progenitor star, suggests that SN 2013dy had a relatively high-metallicity progenitor. Examining one of the largest single set of high-resolution spectra for an SN Ia, we find no evidence of variable absorption from circumstellar material. Combining our UV spectra, NIR photometry, and high-cadence optical photometry, we construct a bolometric light curve, showing that SN 2013dy had a maximum luminosity of <f>$10.0^{+4.8}_{-3.8} \\times 10^{42}$</f> erg s−1. We compare the synthetic light curves and spectra of several models to SN 2013dy, finding that SN 2013dy is in good agreement with a solar-metallicity W7 model.