SN 2017ens: The Metamorphosis of a Luminous Broad-lined Type Ic Supernova into an SN IIn
astro-ph.SR
/ Authors
T. -W. Chen, C. Inserra, M. Fraser, T. J. Moriya, P. Schady, T. Schweyer, A. V. Filippenko, D. A. Perley, A. J. Ruiter, I. Seitenzahl
and 39 more authors
J. Sollerman, F. Taddia, J. P. Anderson, R. J. Foley, A. Jerkstrand, C. -C. Ngeow, Y. -C. Pan, A. Pastorello, S. Points, S. J. Smartt, K. W. Smith, S. Taubenberger, P. Wiseman, D. R. Young, S. Benetti, M. Berton, F. Bufano, P. Clark, M. Della Valle, L. Galbany, A. Gal-Yam, M. Gromadzki, C. P. Gutiérrez, A. Heinze
/ 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 H-alpha and H-beta 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 H-alpha emission persisting at high luminosity (~3x10^40 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.