SN 2017ens: The Metamorphosis of a Luminous Broadlined Type Ic Supernova into an SN IIn

T.-W. Chen*, C. Inserra, M. Fraser, T. J. Moriya, P. Schady, T. Schweyer, A. Filippenko, D. A. Perley, A. J. Ruiter, I. Seitenzahl, J. Sollerman, F. Taddia, J. P. Anderson, R. J. Foley, A. Jerkstrand, C-C Ngeow, Y-C Pan, A. Pastorello, S. Points, S. J. SmarttK. W. Smith, S. Taubenberger, P. Wienlan, D. R. Young, S. Benetti, M. Berton, F. Bufano, P. Clark, M. Della Valle, L. Galbany, A. Gal-Yam, M. Gromadzki, C. P. Gutierrez, A. Heinze, E. Kankare, C. D. Kilpatrick, H. Kuncarayakti, G. Leloudas, Z-Y Lin, K. Maguire, P. Mazzali, O. McBrien, S. J. Prentice, A. Rau, A. Rest, M. R. Siebert, B. Stalder, J. L. Tonry, P.-C. Yu

*Corresponding author for this work

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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 Mg = -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 x 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.
Original languageEnglish
Article numberL31
JournalAstrophysical Journal Letters
Issue number2
Number of pages8
Publication statusPublished - 2018


  • Supernovae: general
  • supernovae: individual (SN 2017ens)


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