Characterization of type Ibn SNe

TL;DR

This study presents the largest systematic analysis of Type Ibn supernovae (SNe Ibn) to date, combining 61 events (24 from Young SNE Experiment data and 37 from the literature) to examine correlations between He I λ5876 spectral features and multi-band light curves, including X-ray data. Using MOSFiT, the authors model 24 well-sampled SNe Ibn under CSI and RD+CSI powering, finding predominantly low ejecta masses (~1 M⊙), compact helium-rich CSM masses (~0.1 M⊙), and explosive energies < 10^51 erg, with CSM densities suggesting wind-like environments (s ≳ 1) and inner CSM radii R0 ≲ 2×10^14 cm for dense cases. Spectroscopy shows a mean narrow He I component velocity around 1100 km/s and a broader component near 5000 km/s, supporting a picture in which most SNe Ibn arise from binary progenitors rather than single very massive Wolf-Rayet stars; this is further supported by X-ray constraints that indicate relatively modest mass-loss rates (~0.1 M⊙/yr) in many cases. The work also reveals significant diversity in light-curve shapes, colors, and line profiles, and emphasizes degeneracies in modeling (notably between ρCSM and R0) and the potential for asymmetric CSM geometries, advocating more sophisticated CSM configurations to fully capture Ibn physics.

Abstract

Type Ibn supernovae (SNe) are characterized by narrow helium (He I) lines from photons produced by the unshocked circumstellar material (CSM). About 80 SNe Ibn have been discovered to date, and only a handful have extensive observational records. Thus, many open questions regarding the progenitor system and the origin of the CSM remain. Here we investigate potential correlations between the spectral features of the prominent He I $λ$5876 line and the optical and X-ray light curve properties of SNe Ibn. We compile the largest sample of 61 SNe Ibn to date, of which 24 SNe have photometric and spectroscopic data from the Young Supernova Experiment and 37 SNe have archival data sets. We fit 24 SNe Ibn with sufficient photometric coverage ($B$ to $z$ bands) using semi-analytical models from MOSFiT. We demonstrate that the light curves of SNe Ibn are more diverse than previous analyses suggest, with absolute $r$-band peak magnitudes of $-19.4\pm0.6$~mag and rise (from $-10$ days to peak) and decay-rates (from peak to +10 days) of $-0.08\pm0.06$ and $0.08\pm0.03$ mag/day, respectively. We find that the majority of SNe Ibn in the sub-sample are consistent with a low-energy explosion ($<10^{51}$ erg) of a star with a compact envelope surrounded by $\sim$0.1 M$_{\odot}$ of helium-rich CSM. The inferred ejecta masses are small ($\sim 1$ M$_{\odot}$) and expand with a velocity of $\sim$5000 km/s. Our spectroscopic analysis shows that the mean velocity of the narrow component of the He I lines, associated to the CSM, peaks at $\sim1100$ km/s. The mean CSM and ejecta masses inferred for a sub-sample of SNe Ibn indicate that their progenitors are not massive ($\sim10$ M$_{\odot}$), single stars at the moment of explosion, but are likely binary systems. This agrees with the detection of potential companion stars of SNe Ibn progenitors, and the inferred CSM properties from stellar evolution models.

Figures (13)

• Figure 1: Visualization of the four different SN Ibn samples (F25, X-RAY, MOSFiT, and Literature) analyzed in this work, with the individual member SN labeled. For details, see Tables \ref{['tab:photo_props']} and \ref{['tab:spectroscopic']}).
• Figure 2: Interpolated $B-V$ (upper panel) and $g-r$ (lower panel) curves for the 24 SNe Ibn from F25 (magenta filled circles), the Icn/Ibn (2023emq-like; yellow filled circles) and the color curves ($\pm1\sigma$) of the Literature (Lit.) sample (blue regions). The color curves ($\pm1\sigma$) of five SNe Icn are included for comparison (red regions). The photometric data of the SNe Icn are retrieved from GalYam_2022Perley_2021cspFraser_2021cspPellegrino_IcnDavis2022ann.
• Figure 3: Upper panel: Absolute $R/r$-band-like light curves of all SNe Ibn from F25 sample that are first reported in this work (magenta dots) and Literature sample (blue lines). Gray (H17) regions correspond to the average light curve and $1.96\sigma$ error bars of 18 type Ibn SNe from Hosseinzadeh_2017. Yellow dots correspond to the likely Icn/Ibn SNe 2023emq Pursiainen_2023, 2023qre, 2023rau and 2023xgo (this work). Red lines correspond to the five Icn SNe discovered up to date. Lower panel: Same as upper panel, with the subtraction of the peak magnitude of each SN. Green (K24) regions correspond to the median light curve and the 25% and 75% percentiles from Somayeh_2024.
• Figure 4: Absolute ($R/r$-band) peak magnitude versus the absolute value of the slope parameters of the ($R/r$-band) light curves ($\gamma$). The SNe Ibn from the F25 and Literature sample are presented as magenta and blue circles, respectively. Panels upper left, upper right, lower left and lower right show the light curve slopes $\gamma_{-10}$ ($-10$ to $t_{\rm max}$), $\gamma_{+10}$ ($t_{\rm max}$ to day $+10$), $\gamma_{+20}$ ($+10$ to $+20$ days), and $\gamma_{+30}$ ($+20$ to $+30$ days), respectively.
• Figure 5: Absolute values of the $R/r$-band slopes $\gamma_{-10}$ ( left panel) and $\gamma_{+20}$ ( right panel) versus $\gamma_{+10}$. The numbers within each plot are the Spearman's coefficients and $p$-values for $\gamma_{-10}$ versus $\gamma_{+10}$ ( left panel) and for $\gamma_{+20}$ versus $\gamma_{+10}$ ( right panel). The SNe Ibn from the F25 and Literature sample are presented as magenta and blue circles, respectively.