More Like this

1. Supernova 2020wnt: An Atypical Superluminous Supernova with a Hidden Central Engine

   https://doi.org/10.3847/1538-4357/acc6c3  

   Tinyanont, Samaporn ; Woosley, Stan E. ; Taggart, Kirsty ; Foley, Ryan J. ; Yan, Lin ; Lunnan, Ragnhild ; Davis, Kyle W. ; Kilpatrick, Charles D. ; Siebert, Matthew R. ; Schulze, Steve ; et al ( June 2023 , The Astrophysical Journal)

   We present observations of a peculiar hydrogen- and helium-poor stripped-envelope (SE) supernova (SN) 2020wnt, primarily in the optical and near-infrared (near-IR). Its peak absolute bolometric magnitude of −20.9 mag (L_{bol, peak}= (6.8 ± 0.3) × 10⁴³erg s⁻¹) and a rise time of 69 days are reminiscent of hydrogen-poor superluminous SNe (SLSNe I), luminous transients potentially powered by spinning-down magnetars. Before the main peak, there is a brief peak lasting <10 days post explosion, likely caused by interaction with circumstellar medium (CSM) ejected ∼years before the SN explosion. The optical spectra near peak lack a hot continuum and Oiiabsorptions, which are signs of heating from a central engine; they quantitatively resemble those of radioactivity-powered hydrogen/helium-poor Type Ic SESNe. At ∼1 yr after peak, nebular spectra reveal a blue pseudo-continuum and narrow Oirecombination lines associated with magnetar heating. Radio observations rule out strong CSM interactions as the dominant energy source at +266 days post peak. Near-IR observations at +200–300 days reveal carbon monoxide and dust formation, which causes a dramatic optical light-curve dip. Pair-instability explosion models predict slow light curve and spectral features incompatible with observations. SN 2020wnt is best explained as a magnetar-powered core-collapse explosion of a 28M_⊙pre-SN star. The explosion kinetic energy is significantly larger than the magnetar energy at peak, effectively concealing the magnetar-heated inner ejecta until well after peak. SN 2020wnt falls into a continuum between normal SNe Ic and SLSNe I, and demonstrates that optical spectra at peak alone cannot rule out the presence of a central engine.

    

   more » « less
2. Peculiar Spectral Evolution of the Type I Supernova 2019eix: A Possible Double Detonation from a Helium Shell on a Sub-Chandrasekhar-mass White Dwarf

   https://doi.org/10.3847/1538-4357/acdd6a  

   Padilla Gonzalez, E. ; Howell, D. Andrew ; Burke, J. ; Dong 董, Yize 一泽 ; Hiramatsu, D. ; McCully, C. ; Pellegrino, C. ; Kerzendorf, W. ; Modjaz, M. ; Terreran, G. ; et al ( July 2023 , The Astrophysical Journal)

   We present photometric and spectroscopic data for the nearby Type I supernova (SN Ia) 2019eix (originally classified as an SN Ic), from the day of its discovery up to 100 days after maximum brightness. Before maximum light, SN 2019eix resembles a typical SN Ic, albeit lacking the usual Oifeature. Its light curve is similar to the typical SN Ic with decline rates (ΔM_15,V= 0.84) and absolute magnitudeM_V= −18.35. However, after maximum light, this SN has unusual spectroscopic features, a large degree of line blending, significant line blanketing in the blue (λ< 5000 Å), and strong Caiiabsorption features during and after peak brightness. These unusual spectral features are similar to models of subluminous thermonuclear explosions, specifically double-detonation models of SNe Ia. Photometrically, SN 2019eix appears to be somewhat brighter with slower decline rates than other double-detonation candidates. We modeled the spectra using the radiative-transfer codeTARDISusing SN 1994I (an SN Ic) as a base model to see whether we could reproduce the unusual features of SN 2019eix and found them to be consistent with the exception of the Oifeature. We also compared SN 2019eix with double-detonation models and found them to best match the observations of SN 2019eix, but failed to reproduce its full photometric and spectroscopic evolution.

    

   more » « less
3. Ultraviolet Spectroscopy and TARDIS Models of the Broad-lined Type Ic Supernova 2014ad

   https://doi.org/10.3847/1538-4357/ac8989  

   Kwok, Lindsey A. ; Williamson, Marc ; Jha, Saurabh W. ; Modjaz, Maryam ; Camacho-Neves, Yssavo ; Foley, Ryan J. ; Garnavich, Peter ; Maeda, Keiichi ; Milisavljevic, Dan ; Pandya, Viraj ; et al ( September 2022 , The Astrophysical Journal)

   Few published ultraviolet (UV) spectra exist for stripped-envelope supernovae and none to date for broad-lined Type Ic supernovae (SNe Ic-bl). These objects have extremely high ejecta velocities and are the only supernova type directly linked to gamma-ray bursts (GRBs). Here we present two epochs of HST/STIS spectra of the SN Ic-bl 2014ad, the first UV spectra for this class. We supplement this with 26 new epochs of ground-based optical spectra, augmenting a rich spectral time series. The UV spectra do not show strong features and are consistent with broadened versions of other SN Ic spectra observed in the UV. We measure Feii5169 Å velocities and show that SN 2014ad has even higher ejecta velocities than most SNe Ic both with and without observed GRBs. We construct models of the SN 2014ad UV+optical spectra usingtardis, a 1D Monte Carlo radiative-transfer spectral synthesis code. The models fit the data well at multiple epochs in the optical but underestimate the flux in the UV, likely due to simplifying assumptions. We find that high densities at high velocities are needed to reproduce the spectra, with ∼3M_⊙of material atv> 22,000 km s⁻¹, assuming spherical symmetry. Our nebular line fits suggest a steep density profile at low velocities. Together, these results imply a higher total ejecta mass than estimated from previous light-curve analysis and expected from theory. This may be reconciled by a flattening of the density profile at low velocity and extra emission near the center of the ejecta.

    

   more » « less
4. SN 2020bio: A Double-peaked, H-poor Type IIb Supernova with Evidence of Circumstellar Interaction

   https://doi.org/10.3847/1538-4357/ace595  

   Pellegrino, C. ; Hiramatsu, D. ; Arcavi, I. ; Howell, D. A. ; Bostroem, K. A. ; Brown, P. J. ; Burke, J. ; Elias-Rosa, N. ; Itagaki, K. ; Kaneda, H. ; et al ( August 2023 , The Astrophysical Journal)

   We present photometric and spectroscopic observations of SN 2020bio, a double-peaked Type IIb supernova (SN) discovered within a day of explosion, primarily obtained by Las Cumbres Observatory and Swift. SN 2020bio displays a rapid and long-lasting initial decline throughout the first week of its light curve, similarly to other well-studied Type IIb SNe. This early-time emission is thought to originate from the cooling of the extended outer hydrogen-rich (H-rich) envelope of the progenitor star that is shock heated by the SN explosion. We compare SN 2020bio to a sample of other double-peaked Type IIb SNe in order to investigate its progenitor properties. Analytical model fits to the early-time emission give progenitor radius (≈100–1500R_⊙) and H-rich envelope mass (≈0.01–0.5M_⊙) estimates that are consistent with other Type IIb SNe. However, SN 2020bio displays several peculiarities, including (1) weak H spectral features indicating a greater amount of mass loss than other Type IIb progenitors; (2) an underluminous secondary light-curve peak that implies a small amount of synthesized⁵⁶Ni (M_Ni≈0.02M_⊙); and (3) low-luminosity nebular [Oi] and interaction-powered nebular features. These observations are more consistent with a lower-mass progenitor (M_ZAMS≈ 12M_⊙) that was stripped of most of its H-rich envelope before exploding. This study adds to the growing diversity in the observed properties of Type IIb SNe and their progenitors.

    

   more » « less
5. SN 2022joj: A Potential Double Detonation with a Thin Helium Shell

   https://doi.org/10.3847/1538-4357/ad19c9  

   Padilla Gonzalez, E. ; Howell, D. A. ; Terreran, G. ; McCully, C. ; Newsome, M. ; Burke, J. ; Farah, J. ; Pellegrino, C. ; Bostroem, K. A. ; Hosseinzadeh, G. ; et al ( March 2024 , The Astrophysical Journal)

   We present photometric and spectroscopic data for SN 2022joj, a nearby peculiar Type Ia supernova (SN Ia) with a fast decline rate (Δm_15,B= 1.4 mag). SN 2022joj shows exceedingly red colors, with a value of approximatelyB−V≈ 1.1 mag during its initial stages, beginning from 11 days before maximum brightness. As it evolves, the flux shifts toward the blue end of the spectrum, approachingB−V≈ 0 mag around maximum light. Furthermore, at maximum light and beyond, the photometry is consistent with that of typical SNe Ia. This unusual behavior extends to its spectral characteristics, which initially displayed a red spectrum and later evolved to exhibit greater consistency with typical SNe Ia. Spectroscopically, we find strong agreement between SN 2022joj and double detonation models with white dwarf masses of around 1M_⊙and a thin He shell between 0.01 and 0.05M_⊙. Moreover, the early red colors are explained by line-blanketing absorption from iron peak elements created by the double detonation scenario in similar mass ranges. The nebular spectra in SN 2022joj deviate from expectations for double detonation, as we observe strong [Feiii] emission instead of [Caii] lines as anticipated, though this is not as robust a prediction as early red colors and spectra. The fact that as He shells get thinner these SNe start to look more like normal SNe Ia raises the possibility that this is the triggering mechanism for the majority of SNe Ia, though evidence would be missed if the SNe are not observed early enough.

    

   more » « less