More Like this

1. SN 2017fzw: A Fast-Expanding Type Ia Supernova with Transitional Features

   https://doi.org/10.3390/universe9060295  

   Huang, Jiayu; Li, Yangyang; Zeng, Xiangyun; Zheng, Sheng; Bird, Sarah A.; Zhang, Jujia; Esamdin, Ali; Iskandar, Abdusamatjan; Bostroem, K. Azaleee; Zeng, Shuguang; et al (June 2023, Universe)

   In this study, we analyzed the optical observations of a subluminous Type Ia supernova (SN Ia) 2017fzw, which exhibited high photospheric velocity (HV) at B-band maximum light. The absolute B-band peak magnitude was determined to be MmaxB=−18.65±0.13 mag, similar to 91bg-like SNe Ia. An estimation of the rate of decline for the B-band light curve was determined to be Δm15(B)=1.60±0.06 mag. The spectra of SN 2017fzw were similar to those of 91bg-like SNe Ia, with prominent Ti ii and Si ii λ5972 features at early phases, gradually transitioning to spectra resembling normal (mainly HV subclass) SNe Ia at later phases, with a stronger Ca ii NIR feature. Notably, throughout all phases of observation, SN 2017fzw displayed spectral evolution characteristics that were comparable to those of HV SNe Ia, and at peak brightness, the Si ii λ6355 velocity was determined to be 13,800 ± 415 km s−1 and a more pronounced Ca ii NIR feature was also detected. Based on these findings, we classify SN 2017fzw as a transitional object with properties of both normal and 91bg-like SNe Ia, providing support for the hypothesis of a continuous distribution of supernovae between these two groups. 

   more » « less
2. Significant luminosity differences of two twin Type Ia supernovae

   https://doi.org/10.1093/mnras/stz3324  

   Foley, Ryan J.; Hoffmann, Samantha L.; Macri, Lucas M.; Riess, Adam G.; Brown, Peter J.; Filippenko, Alexei V.; Graham, Melissa L.; Milne, Peter A. (November 2019, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT The Type Ia supernovae (SNe Ia) 2011by, hosted in NGC 3972, and 2011fe, hosted in M101, are optical ‘twins,’ having almost identical optical light-curve shapes, colours, and near-maximum-brightness spectra. However, SN 2011fe had significantly more ultraviolet (UV; 1600 < λ < 2500 Å) flux than SN 2011by before and at peak luminosity. Several theoretical models predict that SNe Ia with higher progenitor metallicity should (1) have additional UV opacity and thus lower UV flux; (2) have an essentially unchanged optical spectral-energy distribution; (3) have a similar optical light-curve shape; and (4) because of the excess neutrons, produce more stable Fe-group elements at the expense of radioactive 56Ni and thus have a lower peak luminosity. Following these predictions, Foley and Kirshner suggested that the difference in UV flux between SNe 2011by and 2011fe was the result of their progenitors having significantly different metallicities. They also measured a large, but insignificant, difference between the peak absolute magnitudes of the SNe (ΔMV, peak = 0.60 ± 0.36 mag), with SN 2011fe being more luminous. We present a new Cepheid-based distance to NGC 3972, substantially improving the precision of the distance measurement for SN 2011by. With these new data, we determine that the SNe have significantly different peak luminosities (ΔMV, peak = 0.335 ± 0.069 mag). Consequently, SN 2011fe produced 38 per cent more 56Ni than SN 2011by, consistent with predictions for progenitor metallicity differences for these SNe, although alternative models may also explain this difference. We discuss how progenitor metallicity differences can contribute to the intrinsic scatter for light-curve-shape-corrected SN luminosities, the use of ‘twin’ SNe for measuring distances, and implications for using SNe Ia for constraining cosmological parameters. 

   more » « less
3. Carnegie Supernova Project: The First Homogeneous Sample of Super-Chandrasekhar-mass/2003fg-like Type Ia Supernovae

   https://doi.org/10.3847/1538-4357/ac19ac  

   Ashall, C.; Lu, J.; Hsiao, E. Y.; Hoeflich, P.; Phillips, M. M.; Galbany, L.; Burns, C. R.; Contreras, C.; Krisciunas, K.; Morrell, N.; et al (November 2021, The Astrophysical Journal)

   Abstract We present a multiwavelength photometric and spectroscopic analysis of 13 super-Chandrasekhar-mass/2003fg-like Type Ia supernovae (SNe Ia). Nine of these objects were observed by the Carnegie Supernova Project. The 2003fg-like SNe have slowly declining light curves (Δ m 15 ( B ) < 1.3 mag), and peak absolute B -band magnitudes of −19 < M B < −21 mag. Many of the 2003fg-like SNe are located in the same part of the luminosity–width relation as normal SNe Ia. In the optical B and V bands, the 2003fg-like SNe look like normal SNe Ia, but at redder wavelengths they diverge. Unlike other luminous SNe Ia, the 2003fg-like SNe generally have only one i -band maximum, which peaks after the epoch of the B -band maximum, while their near-IR (NIR) light-curve rise times can be ≳40 days longer than those of normal SNe Ia. They are also at least 1 mag brighter in the NIR bands than normal SNe Ia, peaking above M H = −19 mag, and generally have negative Hubble residuals, which may be the cause of some systematics in dark-energy experiments. Spectroscopically, the 2003fg-like SNe exhibit peculiarities such as unburnt carbon well past maximum light, a large spread (8000–12,000 km s −1 ) in Si ii λ 6355 velocities at maximum light with no rapid early velocity decline, and no clear H -band break at +10 days. We find that SNe with a larger pseudo-equivalent width of C ii at maximum light have lower Si ii λ 6355 velocities and more slowly declining light curves. There are also multiple factors that contribute to the peak luminosity of 2003fg-like SNe. The explosion of a C–O degenerate core inside a carbon-rich envelope is consistent with these observations. Such a configuration may come from the core-degenerate scenario. 

   more » « less
4. SN 2020jgb: A Peculiar Type Ia Supernova Triggered by a Helium-shell Detonation in a Star-forming Galaxy

   https://doi.org/10.3847/1538-4357/acbb5e  

   Liu, Chang; Miller, Adam A.; Polin, Abigail; Nugent, Anya E.; De, Kishalay; Nugent, Peter E.; Schulze, Steve; Gal-Yam, Avishay; Fremling, Christoffer; Anand, Shreya; et al (April 2023, The Astrophysical Journal)

   Abstract The detonation of a thin (≲0.03 M ⊙ ) helium shell (He-shell) atop a ∼1 M ⊙ white dwarf (WD) is a promising mechanism to explain normal Type Ia supernovae (SNe Ia), while thicker He-shells and less massive WDs may explain some recently observed peculiar SNe Ia. We present observations of SN 2020jgb, a peculiar SN Ia discovered by the Zwicky Transient Facility (ZTF). Near maximum brightness, SN 2020jgb is slightly subluminous (ZTF g -band absolute magnitude −18.7 mag ≲ M g ≲ −18.2 mag depending on the amount of host-galaxy extinction) and shows an unusually red color (0.2 mag ≲ g ZTF − r ZTF ≲ 0.4 mag) due to strong line-blanketing blueward of ∼5000 Å. These properties resemble those of SN 2018byg, a peculiar SN Ia consistent with an He-shell double detonation (DDet) SN. Using detailed radiative transfer models, we show that the optical spectroscopic and photometric evolution of SN 2020jgb is broadly consistent with a ∼0.95–1.00 M ⊙ (C/O core + He-shell) progenitor ignited by a ≳0.1 M ⊙ He-shell. However, one-dimensional radiative transfer models without non-local-thermodynamic-equilibrium treatment cannot accurately characterize the line-blanketing features, making the actual shell mass uncertain. We detect a prominent absorption feature at ∼1 μ m in the near-infrared (NIR) spectrum of SN 2020jgb, which might originate from unburnt helium in the outermost ejecta. While the sample size is limited, we find similar 1 μ m features in all the peculiar He-shell DDet candidates with NIR spectra obtained to date. SN 2020jgb is also the first peculiar He-shell DDet SN discovered in a star-forming dwarf galaxy, indisputably showing that He-shell DDet SNe occur in both star-forming and passive galaxies, consistent with the normal SN Ia population. 

   more » « less
5. Expanding the parameter space of 2002es-like type Ia supernovae: On the underluminous ASASSN-20jq/SN 2020qxp

   https://doi.org/10.1051/0004-6361/202553687  

   Bose, S; Stritzinger, M D; Ashall, C; Baron, E; Hoeflich, P; Galbany, L; Hoogendam, W B; Jensen, E_A M; Kochanek, C S; Post, R S; et al (July 2025, Astronomy & Astrophysics)

   We present optical photometric and spectroscopic observations of the peculiar Type Ia supernovae (SNe Ia) ASASSN-20jq/SN 2020qxp. It is a low-luminosity object, with a peak absolute magnitude ofM_B = −17.1 ± 0.5 mag, while its post-peak light-curve decline rate of Δm₁₅(B) = 1.35 ± 0.09 mag and color-stretch parameter ofs_BV ⪆ 0.82 is similar to that of normal luminosity SNe Ia. That makes it a prevalent outlier in both the SN Ia luminosity-width and the luminosity-color-stretch relations. The analysis of the early light curves indicates a possible “bump” during the first ≈1.4 days of explosion. ASASSN-20jq synthesized a low radioactive⁵⁶Ni mass of 0.09 ± 0.01 M_⊙. The near-maximum light spectra of the supernova show strong Si IIabsorption lines, indicating a cooler photosphere than normal SNe Ia; however, it lacks Ti IIabsorption lines. Additionally, it shows unusually strong absorption features of O Iλ7773 and the Ca IInear-infrared triplet. The nebular spectra of ASASSN-20jq show a remarkably strong but narrow forbidden [Ca II]λλ7291, 7324 doublet emission that has not been seen in SNe Ia except for a handful of Type Iax events. There is also a marginal detection of the [O I]λλ6300, 6364 doublet emission in nebular spectra, which is extremely rare. Both the [Ca II] and [O I] lines are redshifted by roughly 2000 km s⁻¹. ASASSN-20jq also exhibits a strong [Fe II]λ7155 emission line with a tilted-top line profile, which is identical to the [Fe II]λ16433 line profile. The asymmetric [Fe II] line profiles, along with the redshifted [Ca II] and emission lines, suggest a high central density white dwarf progenitor that underwent an off-center delayed-detonation explosion mechanism, synthesizing roughly equal amounts of⁵⁶Ni during the deflagration and detonation burning phases. The equal production of⁵⁶Ni in both burning phases distinguishes ASASSN-20jq from normal bright and subluminous SNe Ia. Assuming this scenario, we simultaneously modeled the optical and near-infrared nebular spectra, achieving a good agreement with the observations. The light curve and spectroscopic features of ASASSN-20jq do not align with any single sub-class of SNe Ia. However, the significant deviation from the luminosity versus light-curve shape relations (along with several light-curve and spectroscopic features) exhibits similarities to some 2002es-like objects. Therefore, we have identified ASASSN-20jq as an extreme candidate within the broad and heterogeneous parameter space of 2002es-like SNe Ia. 

   more » « less