SN 2022ngb: a faint, slow-evolving Type IIb Supernova with a low-mass envelope

TL;DR

SN 2022ngb is a faint, slow-evolving Type IIb supernova whose photometric and spectroscopic dataset enabled tight constraints on a compact, partially stripped progenitor and an asymmetric explosion. Through multi-band light-curve modelling (Arnett-like and two-component) and NLTE/synthetic-spectra analyses, the authors derive $M_{\mathrm{ej}}\approx3.0\,M_\odot$, $E_{\mathrm{k}}\approx(1.3-3.6)\times10^{51}$ erg, and $M_{\mathrm{Ni}}}\approx0.035$–$0.045\,M_\odot$, with a thin hydrogen envelope of $M_{\mathrm{env}}\approx0.05\,M_\odot$ and $R_{\mathrm{env}}$ of a few $R_\odot$. Nebular-phase spectra reveal asymmetric oxygen and calcium emission, pointing to an aspherical explosion and an anisotropic $^{56}$Ni distribution, consistent with a progenitor near $M_{\mathrm{ZAMS}}\approx15$–$16\,M_\odot$ likely in a binary system. The combined analysis supports a compact, WR-like progenitor with limited envelope, formed via binary interaction, and demonstrates how faint IIb events can still yield robust progenitor constraints through integrated light-curve and nebular spectroscopy modelling.

Abstract

An extensive photometric and spectroscopic follow-up campaign of the Type IIb SN 2022ngb is presented in the article. Through detailed modeling of this dataset, we aim to constrain the key physical parameters of the explosion, infer the nature of the progenitor star and its environment, and probe the dynamical properties of the ejecta. We analyze photometric and spectroscopic data of SN 2022ngb. By constructing and modeling the bolometric light curve with semi-analytic models, we estimate the primary explosion parameters. The spectroscopic data are compared with those of well-studied SNe IIb and NLTE models to constrain the properties of the progenitor and the structure of the resulting ejecta. SN 2022ngb is a low-luminosity SN IIb with a peak bolometric luminosity of L_bol = 7.76 (+1.15/-1.00) x 10^41 erg/s and a V-band rising time of 24.32 +/- 0.50 days. Light curve modeling indicates an ejecta mass of ~2.9-3.2 M_sun, an explosion energy of ~1.4 x 10^51 erg, and a low synthesized 56Ni mass of ~0.045 M_sun. Nebular phase spectra exhibit asymmetric line profiles, pointing to a non-spherical explosion and an anisotropic distribution of radioactive material. Our analysis reveals a relatively compact stripped-envelope progenitor with a pre-SN mass of approximately 4.7 M_sun (corresponding to a 15-16 M_sun ZAMS star). Our analysis suggests that SN 2022ngb originated from the explosion of a moderate-mass relatively compact, stripped-envelope star in a binary system. The asymmetries inferred from the nebular phase spectral line features suggest a non-spherical explosion.

Figures (18)

• Figure 1: Composite BVr-band image constructed from images obtained with the NOT/ALFOSC. The location of SN 2022ngb with the host galaxy UGC 11380.
• Figure 2: Multi-band (optical BgcVroiz and NIR JHK) light curves of SN 2022ngb, showing apparent magnitudes with arbitrary offsets. Different colors and symbols correspond to different photometric filters, as indicated in the legend. The left panel displays the full light curve evolution, while the right panel provides a zoomed-in view of the early-phase light curves. All photometric points include error bars that, in general, are smaller than the marker sizes.
• Figure 3: Absolute V-band light curve of SN 2022ngb compared with other SNe IIb. All light curves have been corrected for reddening and shifted according to the distances listed in Table \ref{['tab_appSNIIbInfo']}.
• Figure 4: Intrinsic color evolution of SN 2022ngb, compared with a sample of SNe IIb. The color curves are corrected for a total line-of-sight extinction. The black lines over-plotted with gray area around represent the color evolution template from Stritzinger2018AA.
• Figure 5: Pseudo-bolometric light curve of SN 2022ngb. Top panels: light curve constructed using optical and NIR data only. Bottom panels: Evolution of the contribution of the individual wavelength ranges (blue corresponds to the optical and the red to NIR) with time of the pseudo-bolometric luminosity. The blue points stand for the pseudo-bolometric light curve solely constructed using optical data, while the red points represent the pseudo-bolometric light curve constructed with optical and NIR data.