SN 2023dbc in M 108: 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, covering a period from 2 to 136 days after the explosion. By comparing its color evolution, specifically in r − JHKs and i − JHKs, with those of broad-lined Type Ic (Ic-BL) and Type IIb SNe, we estimate a significant extinction of AV = 4.1 ± 0.1 mag toward the SN. The extinction-corrected peak absolute magnitudes are MJ = −16.8 ± 0.2 mag, MH = −16.8 ± 0.2 mag, and MKs = −17.0 ± 0.2 mag. The SN exhibited an r-band rise time of 14.9 days. The spectra display broad features indicative of high expansion velocities; the He I line velocity was measured at 16000 km s−1 at t = −4 d. Its spectral profile is broader than those of typical moderately energetic Type Ib SNe, 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 a kinetic energy of Ek = (4.1 ± 0.7) × 1051 erg, an ejecta mass of Mej = 2.3 ± 0.7 M, and a radioactive 56Ni mass of (3.8 ± 0.1) × 10−2 M. An analysis using a two-component model suggests a steep density profile in the outer layer contrasted with a dense inner core, which implies ejecta asphericity. The low 56Ni mass is consistent with a partial fallback scenario. We conclude that SN 2023dbc originated from an aspherical explosion with partial core fallback, arising from a progenitor (Mini 15 M) that had retained its helium envelope within a binary system.