Bridging between Type IIb and Ib Supernovae: SN IIb 2022crv with a Very Thin Hydrogen Envelope

We present optical, near-infrared, and radio observations of supernova (SN) SN IIb 2022crv. We show that it retained a very thin H envelope and transitioned from an SN IIb to an SN Ib; prominent H alpha seen in the pre-maximum phase diminishes toward the post-maximum phase, while He i lines show increasing strength. SYNAPPS modeling of the early spectra of SN 2022crv suggests that the absorption feature at 6200 angstrom is explained by a substantial contribution of H alpha together with Si ii, as is also supported by the velocity evolution of H alpha. The light-curve evolution is consistent with the canonical stripped-envelope SN subclass but among the slowest. The light curve lacks the initial cooling phase and shows a bright main peak (peak M V = -17.82 +/- 0.17 mag), mostly driven by radioactive decay of 56Ni. The light-curve analysis suggests a thin outer H envelope (M env similar to 0.05 M circle dot) and a compact progenitor (R env similar to 3 R circle dot). An interaction-powered synchrotron self-absorption model can reproduce the radio light curves with a mean shock velocity of 0.1c. The mass-loss rate is estimated to be in the range of (1.9-2.8) x 10-5 M circle dot yr-1 for an assumed wind velocity of 1000 km s-1, which is on the high end in comparison with other compact SNe IIb/Ib. SN 2022crv fills a previously unoccupied parameter space of a very compact progenitor, representing a beautiful continuity between the compact and extended progenitor scenario of SNe IIb/Ib.