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Abstract We present SN 2023zaw—a subluminous ( M r = −16.7 mag) and rapidly evolving supernova ( t 1/2, r = 4.9 days), with the lowest nickel mass (≈0.002 M ⊙ ) measured among all stripped-envelope supernovae discovered to date. The photospheric spectra are dominated by broad He i and Ca near-infrared emission lines with velocities of ∼10,000−12,000 km s −1 . The late-time spectra show prominent narrow He i emission lines at ∼1000 km s −1 , indicative of interaction with He-rich circumstellar material. SN 2023zaw is located in the spiral arm of a star-forming galaxy. We perform radiation-hydrodynamical and analytical modeling of the lightcurve by fitting with a combination of shock-cooling emission and nickel decay. The progenitor has a best-fit envelope mass of ≈0.2 M ☉ and an envelope radius of ≈50 R ⊙ . The extremely low nickel mass and low ejecta mass (≈0.5 M ⊙ ) suggest an ultrastripped SN, which originates from a mass-losing low-mass He-star (zero-age main-sequence mass < 10 M ⊙ ) in a close binary system. This is a channel to form double neutron star systems, whose merger is detectable with LIGO. SN 2023zaw underscores the existence of a previously undiscovered population of extremely low nickel mass (<0.005 M ☉ ) stripped-envelope supernovae, which can be explored with deep and high-cadence transient surveys.
Das et al. (Tue,) studied this question.