SN 2020cpg: an energetic link between type IIb and Ib supernovae

Abstract

Stripped-envelope supernovae (SE-SNe) show a wide variety of photometric and spectroscopic properties. This is due to the different potential formation channels and the stripping mechanism that allows for a large diversity within the progenitors outer envelop compositions. Here, the photometric and spectroscopic observations of SN 2020cpg covering $\sim 130$ days from the explosion date are presented. SN 2020cpg ($z=0.037$) is a bright SE-SNe with the $B$-band peaking at $M_B=-17.75\pm 0.39$ mag and a maximum pseudo-bolometric luminosity of $L_{\max }=6.03\pm 0.01\times 10^{42}\mathrm{erg}{\mathrm{s}}^{-1}$. Spectroscopically, SN 2020cpg displays a weak high and low velocity H$\hat{I}\pm$ feature during the photospheric phase of its evolution, suggesting that it contained a detached hydrogen envelope prior to explosion. From comparisons with spectral models, the mass of hydrogen within the outer envelope was constrained to be $\sim 0.1{\mathrm{M}}_{\odot }$. From the pseudo-bolometric light curve of SN 2020cpg a ${}^{56}$Ni mass of $M_{\mathrm{Ni}}\sim 0.27\pm 0.08$ ${\mathrm{M}}_{\odot }$ was determined using an Arnett-like model. The ejecta mass and kinetic energy of SN 2020cpg were determined using an alternative method that compares the light curve of SN 2020cpg and several modelled SE-SNe, resulting in an ejecta mass of $M_{\mathrm{ejc}}\sim 5.5\pm 2.0$ ${\mathrm{M}}_{\odot }$ and a kinetic energy of $E_{\mathrm{K}}\sim 9.0\pm 3.0\times 10^{51}\mathrm{erg}$. The ejected mass indicates a progenitor mass of $18-25{\mathrm{M}}_{\odot }$. The use of the comparative light curve method provides an alternative process to the commonly used Arnett-like model to determine the physical properties of SE-SNe.

19 pages, 10 figures, 7 tables