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

Abstract

We present high-cadence UV, optical, and near-infrared data on the luminous Type II-P supernova SN

2017gmr from hours after discovery through the fi rst 180 days. SN

2017gmr does not show signs of narrow, high-ionization emission lines in the early optical spectra, yet the optical light-curve evolution suggests that an extra energy source from circumstellar medium ( CSM ) interaction must be present for at least 2 days after explosion. Modeling of the early light curve indicates a ∼ 500 R e progenitor radius, consistent with a rather compact red supergiant, and late- time luminosities indicate that up to 0.130

±

0.026 M e of 56 Ni are present, if the light curve is solely powered by radioactive decay, although the 56 Ni mass may be lower if CSM interaction contributes to the post-plateau luminosity. Prominent multipeaked emission lines of H α and [ O I ] emerge after day 154, as a result of either an asymmetric explosion or asymmetries in the CSM. The lack of narrow lines within the fi rst 2 days of explosion in the likely presence of CSM interaction may be an example of close, dense, asymmetric CSM that is quickly enveloped by the spherical supernova ejecta.