SN 2018jmt and SN 2019cj opt and NIR obs. mag.

The spectra indicate that the two SNe exploded within a He-rich circumstellar medium (CSM) lost by the progenitors a short time before the explosion. We model the light curves of the two SNe Ibn to constrain the progenitor and the explosion parameters. The ejecta masses are consistent with either that expected for a canonical SN Ib (~2M_{sun}_) or those from a massive WR star (>~4M_{sun}_), with the kinetic energy on the order of 1051 erg.

The lower limit on the ejecta mass (>~2M_{sun}_) argues against a scenario involving a relatively low-mass progenitor (e.g., MZAMS~10M_{sun}_). We set a conservative upper limit of ~0.1M_{sun}_ for the 56Ni masses in both SNe. From the light curve modelling, we determine a two-zone CSM distribution, with an inner, flat CSM component, and an outer CSM with a steeper density profile.

The physical properties of SN 2018jmt and SN 2019cj are consistent with those expected from the core collapse of relatively massive, stripped-envelope (SE) stars.