SN 2020able Shows Confined CSM Interaction and Stratified He Shells from Late WN Progenitor

{"The transient exploded in SDSS J092602.93+243115.1 at sub-solar metallicity. Early photometry reached 4.4e43 erg/s, requiring efficient kinetic-to-radiative conversion via CSM interaction. Light-curve fits using a thin-shell model constrain the interaction phase to a narrow temporal window, after which the light curve tracks the radioactive decay and expansion of the bare ejecta.","Spectra resolve three velocity components: an inner dense shell at 1.4e9 cm^-3 consistent with a 0.018 solar mass eruptive ejection months before explosion, an outer shell expanding at 1200 km/s matching WR escape velocities, and the shocked interaction zone. These parameters align closely with the pre-SN outburst of SN 2006jc but add a spatially extended outer component absent in that event.","The outer shell velocity and He-rich composition favor a WN-to-WC transition progenitor rather than an LBV or binary channel. This stratified CSM challenges single-star wind models and supports episodic mass loss tied to the final nuclear burning stages. The low host metallicity may enhance such outbursts by reducing line-driven wind efficiency.","Future multi-epoch spectroscopy of new Type Ibn events will test whether discrete shells at 10^15 cm scales are common. Radio and X-ray monitoring can constrain the density profile beyond the optical photosphere and quantify the total pre-SN mass-loss budget."}