SN 2023dbc in M108: Optical and Near-Infrared Observations of a Highly-Obscured, Moderately Energetic Stripped-Envelope Supernova

Abstract

We present near-infrared (NIR) and optical observations of the highly reddened and moderately energetic Type Ib supernova (SN) 2023dbc, {\bf covering a period from} 2 to 136 days after the explosion. By comparing its color {\bf evolution}, specifically in $r-JH{K}_{\mathrm{s}}$ and $i-JH{K}_{\mathrm{s}}$, with those of broad-lined Type Ic (Ic-BL) and Type IIb SNe, we estimate a significant extinction of $A_V=4.1\pm 0.1$\,mag toward the SN. The extinction-corrected peak absolute magnitudes are $M_J=-16.8\pm 0.2$\,mag, $M_H=-16.8\pm 0.2$\,mag, and $M_{K_{\mathrm{s}}}=-17.0\pm 0.2$\,mag. The SN {\bf exhibited} an $r$-band rise time of 14.9 days. The spectra {\bf display} broad features {\bf indicative of} high expansion velocities; the He~{\sc i} line velocity was measured at $16,000\mathrm{km}{\mathrm{s}}^{-1}$ at $t=-4$\,d. Its spectral profile is broader than {\bf those} of typical moderately energetic Type Ib SNe, {\bf yet narrower than those of Type Ic-BL SNe, placing it in an intermediate category}. Based on the light-curve timescale and velocity, we estimate {\bf a} kinetic energy of $E_k=(4.1\pm 0.7)\times 10^{51}$\,erg, {\bf an} ejecta mass of $M_{\mathrm{ej}}=2.3\pm 0.7M_{\odot }$, and a radioactive ${}^{56}\mathrm{Ni}$ mass of $(3.8\pm 0.1)\times 10^{-2}{M}_{\odot }$. {\bf An} analysis using a two-component model suggests a steep density profile in the outer layer {\bf contrasted with} a dense inner core, {\bf which implies} ejecta asphericity. The low ${}^{56}\mathrm{Ni}$ mass is consistent with a partial fallback scenario. We conclude that SN 2023dbc originated from an aspherical explosion with partial core fallback, {\bf arising} from a progenitor ($M_{\mathrm{ini}}\simeq 15M_{\odot }$) that had retained {\bf its} helium envelope {\bf within} a binary system.

12 pages, 8 figures, Accepted for publication in Publications of the Astronomical Society of Japan (PASJ)