Near-infrared and Optical Observations of Type Ic SN 2021krf: Luminous Late-time Emission and Dust Formation

Abstract

We present near-infrared (NIR) and optical observations of the Type Ic supernova (SN Ic) SN 2021krf obtained between days 13 and 259 at several ground-based telescopes. The NIR spectrum at day 68 exhibits a rising K-band continuum flux density longward of ∼2.0 μm, and a late-time optical spectrum at day 259 shows strong [O i] 6300 and 6364 Å emission-line asymmetry, both indicating the presence of dust, likely formed in the SN ejecta. We estimate a carbon-grain dust mass of ∼2 × 10−5 M ⊙ and a dust temperature of ∼900–1200 K associated with this rising continuum and suggest the dust has formed in SN ejecta. Utilizing the one-dimensional multigroup radiation-hydrodynamics code STELLA, we present two degenerate progenitor solutions for SN 2021krf, characterized by C–O star masses of 3.93 and 5.74 M ⊙, but with the same best-fit 56Ni mass of 0.11 M ⊙ for early times (0–70 days). At late times (70–300 days), optical light curves of SN 2021krf decline substantially more slowly than those expected from 56Co radioactive decay. Lack of H and He lines in the late-time SN spectrum suggests the absence of significant interaction of the ejecta with the circumstellar medium. We reproduce the entire bolometric light curve with a combination of radioactive decay and an additional powering source in the form of a central engine of a millisecond pulsar with a magnetic field smaller than that of a typical magnetar.

Supernova Ejecta with Crystalline Silicate Dust in the Supernova Remnant MSH 15–52

“…In the ejecta of SNe IIP, dust starts to form a few hundreds days after SN explosion (Sarangi et al 2018, and references therein). The observations of dust signatures in the SN Ib/c ejecta listed above indicate that the onset of dust formation occurs only 50-70 days after explosion (Di Carlo et al 2008;Smith et al 2008;Rho et al 2021;Ravi et al 2023), with the exception of SN 1990I (∼230 days; Elmhamdi et al 2004). The reason for the early Notes.…”

“…In contrast, few studies thus far have been carried out for dust condensation in the ejecta of SNe Ib/c. Observational signatures of dust formation in the SN Ib/c ejecta have been discovered only for a few SNe in the nebula phase: SN Ib 1990I (Elmhamdi et al 2004), SN Ib(n) 2006jc (Di Carlo et al 2008Smith et al 2008), SN Ic 2020oi (Rho et al 2021), and SN Ic 2021krf (Ravi et al 2023). The molecules that become dust seeds in the SN ejecta and their chemical reactions would not be very different between SNe II and Ib/c, but the environments in which dust condensation occurs would differ depending on SN types and progenitor stars.…”