We present optical and near-infrared observations of a low-luminosity Type IIP supernova ( SN ) 2016bkv from the initial rising phase to the plateau phase . Our observations show that the end of the plateau is extended to \gtrsim \hskip { -2.845276 pt } 140 days since the explosion , indicating that this SN takes one of the longest time to finish the plateau phase .
among Type IIP SNe ( SNe IIP ) , including low-luminosity ( LL ) SNe IIP . The line velocities of various ions at the middle of the plateau phase are as low as 1,000–1,500 km s ^ { -1 } , which is the lowest even among LL SNe IIP .
These measurements imply that the ejecta mass in SN 2016bkv is larger than that of the well-studied LL IIP SN 2003Z .
In the early phase , SN 2016bkv shows a strong bump in the light curve .
In addition , the optical spectra in this bump phase exhibit a blue continuum accompanied with a narrow H \alpha emission line .
These features indicate an interaction between the SN ejecta and the circumstellar matter ( CSM ) as in SNe IIn .
Assuming the ejecta-CSM interaction scenario , the mass loss rate is estimated to be \sim \hskip { -2.845276 pt } 1.7 \times 10 ^ { -2 } ~ { } M _ { \odot } yr ^ { -1 } within a few years before the SN explosion .
This is comparable to or even larger than the largest mass loss rate observed for the Galactic red supergiants ( \sim \hskip { -2.845276 pt } 10 ^ { -3 } ~ { } M _ { \odot } yr ^ { -1 } for VY CMa ) .
We suggest that the progenitor star of SN 2016bkv experienced a violent mass loss just before the SN explosion .