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.
