Extensive Spectroscopy and Photometry of the Type IIP Supernova 2013ej

Abstract

We present extensive optical ($UBVRI$, $g^{\prime }{r}^{\prime }{i}^{\prime }{z}^{\prime }$, and open CCD) and near-infrared ($ZYJH$) photometry for the very nearby Type IIP SN ~2013ej extending from +1 to +461 days after shock breakout, estimated to be MJD $56496.9\pm 0.3$. Substantial time series ultraviolet and optical spectroscopy obtained from +8 to +135 days are also presented. Considering well-observed SNe IIP from the literature, we derive $UBVRIJHK$ bolometric calibrations from $UBVRI$ and unfiltered measurements that potentially reach 2\% precision with a $B-V$ color-dependent correction. We observe moderately strong Si II $\lambda 6355$ as early as +8 days. The photospheric velocity ($v_{\mathrm{ph}}$) is determined by modeling the spectra in the vicinity of Fe II $\lambda 5169$ whenever observed, and interpolating at photometric epochs based on a semianalytic method. This gives $v_{\mathrm{ph}}=4500\pm 500$ km s${}^{-1}$ at +50 days. We also observe spectral homogeneity of ultraviolet spectra at +10--12 days for SNe IIP, while variations are evident a week after explosion. Using the expanding photosphere method, from combined analysis of SN 2013ej and SN 2002ap, we estimate the distance to the host galaxy to be $9.0_{-0.6}^{+0.4}$ Mpc, consistent with distance estimates from other methods. Photometric and spectroscopic analysis during the plateau phase, which we estimated to be $94\pm 7$ days long, yields an explosion energy of $0.9\pm 0.3\times 10^{51}$ ergs, a final pre-explosion progenitor mass of $15.2\pm 4.2$~M${}_{\odot }$ and a radius of $250\pm 70$~R${}_{\odot }$. We observe a broken exponential profile beyond +120 days, with a break point at +$183\pm 16$ days. Measurements beyond this break time yield a ${}^{56}$Ni mass of $0.013\pm 0.001$~M${}_{\odot }$.

29 pages, 23 figures, 15 tables, Published in The Astrophisical Journal