Short-Lived Circumstellar Interaction in a Low-Luminosity Type IIP Supernova

While interaction with circumstellar material is known to play an important role in Type IIn supernovae, analyses of the more common Type IIP and IIL supernovae have not traditionally included interaction as a significant power source. However, recent campaigns to observe supernovae within days of explosion have revealed narrow emission lines of high-ionization species in the earliest spectra of luminous Type II supernovae of all subclasses. These "flash spectroscopy" features indicate the presence of a confined shell of material around the progenitor star. Here we present the first low-luminosity supernova to show flash spectroscopy features, SN 2016bkv. This supernova peaked at M_V = -16 mag and has expansion velocities around maximum light of < 2000 km s^-1, placing it at the faint/slow end of the distribution of Type IIP supernovae (similar to SN 2005cs). The detection of flash spectroscopy features in this event demonstrates that circumstellar interaction plays a role even in a low-luminosity Type IIP supernovae. Conversely, it implies that the range of luminosities of Type II supernovae is not solely driven by the presence of circumstellar material.