We present high-cadence ultraviolet ( UV ) , optical , and near-infrared ( NIR ) data on the luminous Type II-P supernova SN 2017gmr from hours after discovery through the first 180 days .
SN 2017gmr does not show signs of narrow , high-ionization emission lines in the early optical spectra , yet the optical lightcurve 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 lightcurve indicates a \sim 500R _ { \sun } progenitor radius , consistent with a rather compact red supergiant , and late-time luminosities indicate up to 0.130 \pm 0.026 M _ { \sun } of ^ { 56 } Ni are present , if the lightcurve is solely powered by radioactive decay , although the ^ { 56 } Ni mass may be lower if CSM interaction contributes to the post-plateau luminosity .
Prominent multi-peaked emission lines of H \alpha 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 first two 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 .