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SN 2020zbf is a hydrogen-poor superluminous supernova (SLSN) atz = 0.1947 that shows conspicuous C IIfeatures at early times, in contrast to the majority of H-poor SLSNe. Its peak magnitude isMg = −21.2 mag and its rise time (≲26.4 days from first light) places SN 2020zbf among the fastest rising type I SLSNe. We used spectra taken from ultraviolet (UV) to near-infrared wavelengths to identify spectral features. We paid particular attention to the C IIlines as they present distinctive characteristics when compared to other events. We also analyzed UV and optical photometric data and modeled the light curves considering three different powering mechanisms: radioactive decay of56Ni, magnetar spin-down, and circumstellar medium (CSM) interaction. The spectra of SN 2020zbf match the model spectra of a C-rich low-mass magnetar-powered supernova model well. This is consistent with our light curve modeling, which supports a magnetar-powered event with an ejecta massMej = 1.5 M⊙. However, we cannot discard the CSM-interaction model as it may also reproduce the observed features. The interaction with H-poor, carbon-oxygen CSM near peak light could explain the presence of C IIemission lines. A short plateau in the light curve around 35–45 days after peak, in combination with the presence of an emission line at 6580 Å, can also be interpreted as being due to a late interaction with an extended H-rich CSM. Both the magnetar and CSM-interaction models of SN 2020zbf indicate that the progenitor mass at the time of explosion is between 2 and 5M⊙. Modeling the spectral energy distribution of the host galaxy reveals a host mass of 108.7M⊙, a star formation rate of 0.24−0.12+0.41M⊙yr−1, and a metallicity of ∼0.4Z⊙.
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This content will become publicly available on February 24, 2027
Hydrogen-poor Superluminous Supernovae in the Nebular Phase: Spectral Diversity Due to Ejecta Ionization as a Probe of the Power Source
Abstract We present a large sample of 39 nebular-phase optical spectra of 25 hydrogen-poor superluminous supernovae (SLSNe-I) and jointly analyze them with previously published spectra of 12 events. We measure the properties of key emission features, namely, those at 6300, 7300, and 7774 Å (associated with [Oi], [Caii]/[Oii], and Oi, respectively), and find that SLSNe exhibit much wider spectral diversity than normal SNe Ic, primarily in the line ratioL7300/L6300, which is highly sensitive to ejecta ionization. Some events exhibit weak [Oi] and a clear [Oii] contribution to the 7300 Å feature, enhancing the ratio, along with [Oiii] lines at 4363 and 5007 Å. Other SLSNe show weak or no lines of ionized oxygen. Moreover, we find that the population exhibits decreasingL7300/L6300over time, while a few outliers instead display sustained high or increasing ratios for extended periods. The ratioL7300/L6300is also correlated with the rise and decline times of the light curves, with slower events exhibiting higher ionization, the first robust connection between early light-curve and late-time spectral properties, likely due to the magnetar’s impact: slower-evolving SLSNe are generally powered by engines with longer spin-down timescales, which deposit more energy at later phases. Among the events with decreasingL7300/L6300, SLSNe with high ionization are on average powered by magnetars with higher thermalized spin-down power, a correlation that is most significant for events withMej ≲ 12M⊙. The ionization in the outliers with increasingL7300/L6300may be due to late circumstellar medium interaction.L7300/L6300and its evolution are therefore key diagnostics of SLSN engines and progenitor mass loss.
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- Award ID(s):
- 2224255
- PAR ID:
- 10707990
- Publisher / Repository:
- The Astrophysical Journal
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 999
- Issue:
- 1
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 59
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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