SN 2017gmr: An Energetic Type II-P Supernova with Asymmetries

Abstract

We present high-cadence ultraviolet (UV), optical, and near-infrared (NIR)\ndata on the luminous Type II-P supernova SN 2017gmr from hours after discovery\nthrough the first 180 days. SN 2017gmr does not show signs of narrow,\nhigh-ionization emission lines in the early optical spectra, yet the optical\nlightcurve evolution suggests that an extra energy source from circumstellar\nmedium (CSM) interaction must be present for at least 2 days after explosion.\nModeling of the early lightcurve indicates a ~500R$_{\\odot}$ progenitor radius,\nconsistent with a rather compact red supergiant, and late-time luminosities\nindicate up to 0.130 $\\pm$ 0.026 M$_{\\odot}$ of $^{56}$Ni are present, if the\nlightcurve is solely powered by radioactive decay, although the $^{56}$Ni mass\nmay be lower if CSM interaction contributes to the post-plateau luminosity.\nProminent multi-peaked emission lines of H$\\alpha$ and [O I] emerge after day\n154, as a result of either an asymmetric explosion or asymmetries in the CSM.\nThe lack of narrow lines within the first two days of explosion in the likely\npresence of CSM interaction may be an example of close, dense, asymmetric CSM\nthat is quickly enveloped by the spherical supernova ejecta.\n