SN 2017ens: The metamorphosis of a luminous broadlined type Ic supernova into an SN IIn

Chen, T.W., Inserra, C., Fraser, M., Moriya, T.J., Schady, P., Schweyer, T., Filippenko, A.V., Perley, D.A., Ruiter, A.J., Seitenzahl, I., Sollerman, J., Taddia, F., Anderson, J.P., Foley, R.J., Jerkstrand, A., Ngeow, C.C., Pan, Y.C., Pastorello, A., Points, S., Smartt, S.J., Smith, K.W., Taubenberger, S., Wiseman, P., Young, D.R., Benetti, S., Berton, M., Bufano, F., Clark, P., Valle, M. Della, Galbany, L., Gal-Yam, A., Gromadzki, M., Gutiérrez, C.P., Heinze, A., Kankare, E., Kilpatrick, C.D., Kuncarayakti, H., Leloudas, G., Lin, Z.Y., Maguire, K., Mazzali, P., McBrien, O., Prentice, S.J., Rau, A., Rest, A., Siebert, M. R., Stalder, B., Tonry, J.L. and Yu, P.C. (2018) SN 2017ens: The metamorphosis of a luminous broadlined type Ic supernova into an SN IIn. Astrophysical Journal Letters, 867 (2), [L31]. (doi:10.3847/2041-8213/aaeb2e).

Abstract

We present observations of supernova (SN) 2017ens, discovered by the ATLAS survey and identified as a hot blue object through the GREAT program. The redshift z = 0.1086 implies a peak brightness of M _g = -21.1 mag, placing the object within the regime of superluminous supernovae. We observe a dramatic spectral evolution, from initially being blue and featureless, to later developing features similar to those of the broadlined Type Ic SN 1998bw, and finally showing ∼2000 km s^-1 wide Hα and Hβ emission. Relatively narrow Balmer emission (reminiscent of a SN IIn) is present at all times. We also detect coronal lines, indicative of a dense circumstellar medium. We constrain the progenitor wind velocity to ∼50-60 km s^-1 based on P-Cygni profiles, which is far slower than those present in Wolf-Rayet stars. This may suggest that the progenitor passed through a luminous blue variable phase, or that the wind is instead from a binary companion red supergiant star. At late times we see the ∼2000 km s^-1 wide Hα emission persisting at high luminosity (∼3 × 10⁴⁰ erg s^-1) for at least 100 day, perhaps indicative of additional mass loss at high velocities that could have been ejected by a pulsational pair instability.

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Contributors

Author: C. Inserra

Author: P. Wiseman

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