Long-term evolution of the SN 2009ip-like transient SN 2016cvk

The interacting transient SN 2016cvk (ASASSN-16jt) is a peculiar SN 2009ip-like event. We present our follow-up data with an aim to draw conclusions on the physical nature of the progenitor system. Our spectrophotometric data set of SN 2016cvk covers the ultraviolet, optical, and near-infrared wavelength region extending to $+1681,d from the light curve peak. In this work, we analysed the data and made comparison with other SN 2009ip-like transients. We note that archival data reveal pre-outbursts of the progenitor with the first detection at -$1219 d. The light-curve evolution of SN 2016cvk consists of two consecutive luminous events A and B, with peak magnitudes of M_V < -15.6 and M_r = -18.3 mag, respectively. The spectra are dominated by Balmer emission lines that have a complex, multi-component evolution resembling that of other SN 2009ip-like targets. SN 2016cvk is among the first detected SN 2009ip-like events that show early `flash ionisation' features of C iii N iii and He ii lasting for $16 ± 5$ d. Our late-time +405 d spectrum shows forbidden Ca ii Fe ii and O i features, with the latter detected particularly clearly for a SN 2009ip-like event. The evolution of SN 2016cvk is similar to other SN 2009ip-like transients, with some uncommon traits. The lack of a double-peaked structure in the Balmer lines is likely caused by differences in the circumstellar medium structure or viewing angle. The flash features in the early spectra propose abundances consistent with a red, yellow, or blue supergiant progenitor, rather than a luminous blue variable, for example. The detection of O i in the +405 d spectrum suggests some possible evidence of nucleosynthesised material generated in a SN explosion.