SN 2024abvb: A Type Icn Supernova in the Outskirts of its Host Galaxy

Abstract

We present multiband photometric and spectroscopic observations of supernova (SN) 2024abvb, which exhibits early-time prominent photoionized narrow emission lines of C II superposed on a blue continuum. The absence of Balmer features indicates that the SN exploded within hydrogen-poor circumstellar matter (CSM). Together with the lack of explicit evidence of helium signatures, we tentatively identify SN 2024abvb as a Type Icn SN (SN Icn). After correcting for extinction, we estimate an r-band peak absolute magnitude of -19.7, placing SN 2024abvb in the luminous regime of SNe Icn. We adopted a hybrid model that accounts for both the energy released by the ejecta-CSM interaction and the radioactive decay of nickel synthesized in the SN ejecta to fit the light curve of SN 2024abvb. The best-fit model to the multiband light curves within the first ~ 40 days after explosion suggests that the CSM, radioactive nickel, and ejecta masses to be 0.28 Msun, < 3.8 * 10^-2 Msun, and 0.12 Msun, respectively. Such a low ejecta mass indicates that the progenitor star of SN 2024abvb experienced a significant mass-stripping process, consistent with the hydrogen-poor and helium-poor spectral features. SN 2024abvb provides important insights into the physical origins of the rare subclass of SNe Icn.

Figures (9)

• Figure 1: Panel (a): TNOT $r$-band image showing the location of SN 2024abvb. The black dashed square outlines the sky regions displayed in panels (b), (c), and (d), which show respectively the latest $c$-band prediscovery image, and the $c$- and $o$-band first-detection images obtained by ATLAS. Epochs are labeled in the upper right of each panel.
• Figure 2: Multiband light curves of SN 2024abvb. The bandpass of each light curve is marked next to the color-coded symbols, and instruments used to obtain the photometry are indicated by the legend. The open upside-down triangles show the latest nondetection limits in the ATLAS $c$ and $o$ bands. The black curve and the color-shaded region underlying the photometry for each band provide the smoothed light curve and its associated uncertainty, respectively, obtained via a Gaussian process. The phase is relative to the $r$-band peak light of SN 2024abvb.
• Figure 3: Spectral time series of SN 2024abvb acquired by NOT, LJT, XLT, and Lick 3 m Shane from approximately days $-3$ to $+$18 relative to the time of $r$-band maximum brightness (see Sec \ref{['Sec3.1']}). All data are presented with 50 Å binning. The gray, purple, orange, and pink curves show the spectra obtained by NOT, LJT, XLT, and Shane, respectively. The vertical dashed lines indicate the spectral lines of C II and He I. The machine-readable table of the listed spectra is available online.
• Figure 4: Upper and middle panels: the $r$- and $g$-band light curves of SN 2024abvb compared to those of other well-sampled SNe Icn, including SNe 2019hgp 2022Natur.601..201G, 2019jc 2022ApJ...938...73P, 2021ckj 2022ApJ...938...73P2023AA...673A..27N, 2021csp 2022ApJ...927..180P2022ApJ...938...73P, and 2022ann 2023MNRAS.523.2530D. The gray-shaded area presents the template light curve derived by averaging a sample of SNe Ibn 2017ApJ...836..158H. Lower panel: comparison of the $g-r$ color of SN 2024abvb and other SNe Icn. The phase of SN 2024abvb is relative to its $r$-band maximum light, and other objects are from their references. Note that the light curve of each SN has been corrected for reddening, and all phases have been corrected for time dilation caused by the redshift.
• Figure 5: Evolution of C II emission lines of SN 2024abvb in velocity space relative to their rest-frame wavelengths. The dark-blue lines represent the arbitrarily scaled flux spectra in full resolution. The brown curves display the smoothed spectra. Phases are labeled on the right. Vertical pink lines mark the rest-frame wavelengths of the C II lines of interest. For illustration, the vertical dashed blue line in the left panel indicates the rest-frame wavelength of He I$\lambda5876$.