From out of the Blue: Swift Links 2002es-like, 2003fg-like, and Early Time Bump Type Ia Supernovae

In the top row of Figure 2, Group 2 SNe Ia are bluer than Group 1 SNe Ia in the UVW2 − UVW1 and UVM2 − UVW1 color curves, whereas in the UVW2 − UVM2 Group 2 SNe Ia are redder. This is due to the dilution of the UV excess due to the Swift UVW2 filter transmission, i.e., the same amount of UV flux in the UVW2 filter will have a small effect on the UV+optical flux, whereas the excess flux is a larger percentage in the UVM2 filter. In the UVW2 − UVM2 color curve, Group 2 SNe Ia have (UVW2 − UVM2) > − 0.2 mag from explosion to ${t}_{B}^{\max }$. After ${t}_{B}^{\max }$, these same SNe Ia remain redder than other SNe Ia.

While Group 2 SNe Ia are slightly separated from the rest of the sample in the UVW2 − UVW1 color curve, they are closer to the rest of the sample in UVW2 − UVW1 than UVW2 − UVM2 and UVM2 − UVW1.

The increased similarity between Group 1 and Group 2 SNe Ia in the UVW2 − UVW1 color curve may originate from the red leak. In extreme cases, the optical component from the red leak provides over half of the total flux (e.g., Brown et al. 2010). Thus, contamination from optical light dilutes the observed difference from additional UV flux. The difference is still observed with filters with the red leak, demonstrating that abnormal behavior does not arise from the red leak.

The UVW2 − U/B/V color curves are all characterized by the same rapid redward ascent of Group 2 SNe Ia. Prior to t_B ^max, Group 2 SNe Ia are all ≲2.6 mag, whereas Group 1 SNe Ia have 2.5 mag ≤ (UVW2 − U) ≤ 3.5 mag. After ${t}_{B}^{\max }$, Group 2 SNe Ia are on the blue edge of the Group 1 distribution. Like the UVW2 − U/B/V color curves, Group 2 SNe Ia become similar to the rest of our sample in the UVW1 − U/B/V shortly after explosion. Overall, the UVW1 colors evolve in the same manner as the UVW2 filter.

Because the UVM2 filter does not have a red leak, this filter is the best UV probe, so the UVM2 − U/B/V color curves are the most important to consider. Like the other UV−optical colors, Group 2 SNe Ia quickly rise redward in the UVM2 − U/B/V color curves, initially dominated by the UV. The UVM2 − U color curve shows that, even at t_B ^max, Group 2 SNe Ia have different colors, and this difference persists until t ≈ + 15 days. The UVM2 − B and UVM2 − V color curves are generally similar to the UVM2 − U color curve.

For the UVM2 − U color, we compute the significance of observing a color difference between 2002es-like and 2003fg-like SNe Ia and the other spectral subtypes in the −12 ≤ t ≤ − 8 days range. The color range for the rest of our sample is 4.79 ± 1.42 mag. For each of the 2002es-like and 2003fg-like SNe Ia, we compute the significance of the difference between the rest of the sample and the individual SN Ia. For example, the UVM2 − U color for iPTF14atg is 1.30 ± 0.17 mag, which means there is a 2.44σ tension between the average of the rest of the sample and iPTF14atg. This calculation is repeated for each SN Ia. The sum of the significance values is the composite significance (see Fisher 1970), which is ∼13.9σ. Finally, we use the same method to compute the average UVM2 − U color for the 2002es-like and 2003fg-like SNe Ia gives values of 1.51 ± 0.33 mag and 1.73 ± 0.43 mag, respectively. These values are consistent with each other, confirming the visual evidence that these subtypes have matching UV colors. Figure 3 shows the median color evolutions for the Group 1 and Group 2 SNe Ia. Table 2 compiles the median color values calculated from the method above for all filter combinations.

There are two phenomena in the optical color curves shown in the bottom row of Figure 2. First, Group 2 SNe Ia are not as uniform as in the UV, and second, Group 2 SNe Ia are not wholly different than Group 1 SNe Ia near and after ${t}_{B}^{\max }$.

There are several interesting features in the optical colors. First, in the U − B and U − V colors, SN 2019yvq is redder than other Group 2 SNe Ia. As the ejecta slow, they are less blueshifted, so absorption features in the B and V bands become split between the bands, causing SN 2019yvq to appear redder than the other Group 2 SNe Ia. Second, iPTF14atg evolves similarly to SN 2019yvq when −15 ≤ t ≤ − 7 days, but then evolves similarly to the other Group 1 members when t ≥ − 7. Either SN 2019yvq is evolving on an earlier timescale than the other bump SNe Ia and other early time SNe Ia, similar to the V − r color evolution in subluminous SNe Ia (see Figure 8 in Hoogendam et al. 2022), or the mechanism driving the first inflection point in the U − B and U − V colors for iPTF14atg may be absent from SN 2019yvq. Finally, in the B − V color curve, it is difficult to differentiate Group 2 SNe Ia and the 2003fg-like SNe Ia from Group 1 SNe Ia in our sample.

We separate the rising light curves of SNe Ia into three categories as shown in Figure  4: "single," "double," and "bump." Single SNe Ia have rising light curves well fit by a single power law, whereas double SNe Ia have rising light curves better fit by a broken or two-component power law. Bump SNe Ia have nonmonotonic light-curve bumps in the UV and/or the optical (i.e., the flux decreases by at least 1σ between any two epochs during the light-curve rise). Figure 4 and the left-hand panel of Figure 5 elucidate these different rising light-curve behaviors using idealized and observed light curves, respectively. The SNe Ia with bluer UV colors, iPTF14atg, SN 2019yvq, SN 2020hvf, SN 2021zny, and SN 2022ilv, are the only bump SNe Ia, and no spectroscopically normal SNe Ia display bumps by our definition in their rising light curve, despite composing the majority of our sample and the majority of SN Ia volumetrically (Desai et al. 2023). Thus, the color scheme in Figures 1–3 also correlates with rising light-curve morphology. The blue and orange points correspond to SNe Ia with a rising light-curve bump, and the gray points correspond to SNe Ia without a rising light-curve bump. Figure 6 shows the color evolution in the UVM2-UVW1 and B-V colors for SNe Ia categorized by rising light curve. The bump SNe Ia have much bluer UV colors than SNe Ia without a rising light curve bump. However, we note that simultaneous high-cadence, high-S/N, early time optical and UV data do not exist for most of the SNe in our sample since the current observations come from heterogeneous survey and follow-up efforts. For example, there are no simultaneous UV observations of 2003fg-like SNe Ia since all the bumps are observed in the optical. Conversely, both 2002es-like SNe Ia in our sample have observed UV bumps, but iPTF14atg does not show a clear bump in its optical light curves due to a gap in ground-based optical coverage at these epochs and low S/N in in the Swift optical observations. Ultimately, simultaneous high-cadence, high-S/N optical and UV data are needed for further study of SNe Ia rising light curves.

Zoom In Zoom Out Reset image size

Zoom In Zoom Out Reset image size

When considering the colors of the bump SNe Ia, the observed dichotomy of UV colors is inconsistent with the excess luminosity originating from interaction with a companion, which is viewing-angle dependent (Kasen 2010; Brown et al. 2012). This implies companion interaction and other viewing-angle-dependent models are insufficient to explain both two-component rising light curves and rising light curve bumps. Thus, monotonically and nonmonotonically rising light curves may have different physical origins. Despite our small sample, we can disfavor companion interaction as the cause of the early time light-curve bumps. Using the same viewing-angle argument as Burke et al. (2021), the probability of observing bumps in five out of five 2002es-like and 2003fg-like SNe Ia is 1 in 10⁵. Underlying this claim is the assumption that the viewing angle is independent of the spectral subtype, which seems likely to be true, but observations do not guarantee this is reality, and that the companion interaction results in the observables predicted by Kasen (2010). Thus, at the population level, the observed rate of SNe Ia with rising light-curve bumps is too high to be fully explained by companion interaction.

Zoom In Zoom Out Reset image size

Intriguingly, SN 2020hvf, SN 2021zny, and SN 2022ilv all display rising light-curve bumps (Jiang et al. 2021; Dimitriadis et al. 2023; Srivastav et al. 2023b), and Figure 2 shows that the color evolutions of SN 2020hvf, SN 2021zny, and SN 2022ilv are consistent with the regular 2003fg-like SNe Ia in our comparison sample. This would naively suggest that other 2003fg-like SNe Ia have unobserved early time light-curve bumps. Such a conclusion remains speculative due to the small sample size. An initial analysis of SN 2022pul suggests there may not be a rising light-curve bump (Kwok et al. 2023; Siebert et al. 2024), but an in-depth study of the rising light curve is yet to be published. Similarly, iPTF14atg, SN 2019yvq are the only 2002es-like SNe Ia with UV data observed early enough to detect a bump. Three other 2002es-like SNe Ia, iPTF14dpk (Cao et al. 2016; Burke et al. 2021), SN 2022ywc (Srivastav et al. 2023a), and SN 2022vqz (Xi et al. 2024), have reported rising light-curve bumps but no UV data. While the current sample is small, we can obtain preliminary statistical conclusions despite the small number statistics.

Assuming the SNe Ia in our sample are representative, we can compute the minimum fraction of 2002es-like and 2003fg-like SNe Ia that display a rising light-curve bump at a 90% confidence level using binomial statistics. Given b detected bumps from n SNe Ia, what is the minimum percent of the population that has detectable bumps such that there is only a 10% chance of the observations randomly occurring? For 2002es-like SNe Ia, observing 2 rising light-curve bumps from our two-object sample implies that at least 32% of early time 2002es-like SN Ia light curves display a rising light-curve bump. Similarly, for our sample of 2003fg-like SNe Ia, at least 47% of 2003fg-like SNe Ia display a rising light-curve bump (b = n = 3). Combining our sample of 2002es-like and 2003fg-like SNe Ia and assuming 2002es-like and 2003fg-like SNe Ia arise from the same distribution, then, at least 63% of the SNe Ia display a rising light-curve bump (b = n = 5). Finally, if we include 2002es-like and 2003fg-like SNe Ia that lack UV data in our statistical analysis, then, eight out of nine SNe display a rising light-curve bump, and thus, at least 65% of SNe Ia in these subtypes display a rising light-curve bump.

Brown et al. (2014b) show that 2003fg-like SNe Ia are different from normal and 1991T-like SNe Ia in the UVW1 − V and UVM2 − UVW1 colors. This work expands that analysis with color evolution data at t ≤ − 10 days for more SNe Ia and the inclusion of three additional 2003fg-like SNe Ia and two 2002es-like SNe Ia.

There are several observational similarities between 2002es-like and 2003fg-like SNe Ia. Both classes lack a secondary i-band maximum (Ashall et al. 2021; Burke et al. 2021), have some members with nebular [O i] emission (Taubenberger et al. 2013a, 2013b, 2019; Kromer et al. 2016; Dimitriadis et al. 2023; Siebert et al. 2024), and have members with C ii absorption of varying strengths in their near-peak optical spectra (Kromer et al. 2013; Cao et al. 2015; Ashall et al. 2021; Li et al. 2023; Siebert et al. 2024). Lastly, 2003fg-like SNe Ia prefer metal-poor, young environments (e.g., Lu et al. 2021; L. Galbany et al. 2024, in preparation), whereas White et al. (2015) suggest 2002es-like SNe Ia prefer older, elliptical galaxies, but an in-depth study has not yet been performed for the local environments of 2002es-like SNe Ia.

Of the observational similarities between the two subtypes, the shared carbon absorption is perhaps the most intriguing. One proposed source for the C ii feature is a C-rich envelope from the merger of either two CO WDs in the DD scenario (e.g., Raskin & Kasen 2013; Moll et al. 2014; Raskin et al. 2014) or a CO WD and an AGB core in the CD scenario where the AGB star has lost its H and/or He envelope (e.g., Hsiao et al. 2020; Ashall et al. 2021; Lu et al. 2021). Ashall et al. (2021) find a weak linear relationship between the psuedo-equivalent width (pEW) of C ii λ6580 Å and Δm₁₅(B) where faster-declining 2003fg-like SNe Ia have a smaller pEW value. Therefore, if there is a link between the progenitor scenario and/or explosion mechanism of 2002es-like and 2003fg-like SNe Ia, one may expect 2002es-like SNe Ia to follow this relationship with 2002es-like SNe Ia showing weak C ii features.

Observationally, only some 2002es-like SNe Ia display C ii absorption (e.g., SN 2010lp, Kromer et al. 2013; iPTF14atg, Cao et al. 2015; and SN 2016ije, Li et al. 2023), while others completely lack C ii (e.g., PTF10ops, Maguire et al. 2011; PTF10ujn, White et al. 2015; PTF10acdh, White et al. 2015; and SN 2019yvq, Miller et al. 2020). However, 2002es-like SNe Ia without C ii may still have an envelope, which could be observed in a lower-ionization state of carbon. C i λ10693 Å is the strongest C i feature, and a visual inspection of Figure 2 in Burke et al. (2021) suggests the presence of C i in SN 2019yvq. Unfortunately, no other 2002es-like SNe Ia have published near-IR (NIR) spectra near peak light.

If we assume 2002es-like and 2003fg-like SNe Ia are linked, different scenarios can be constructed to explain a potential continuum in either the DD scenario or the CD scenario. The first-order explosion parameters would be the mass of the carbon envelope and the mass of the primary degenerate object (CO WD or CO AGB core, depending on the progenitor scenario). We do not consider potential higher-order effects such as flame speed or burning efficiency in our brief qualitative comparisons.

A larger core mass will produce a more optically luminous explosion with higher ionization features. In this picture, 2002es-like SNe Ia will have smaller core masses because they have lower optical luminosities (see Figure 1) and show lower-ionization lines (e.g., Taubenberger 2017), and conversely, 2003fg-like SNe Ia will have larger core masses due to their larger optical luminosities (see Figure 1) and higher-ionization spectral features (e.g., Taubenberger 2017). Less massive circumstellar material results in weaker C features (i.e., smaller pEWs) since these features trace envelope mass (Ashall et al. 2021), whereas a larger envelope should produce stronger C ii and C i absorption, more luminous peak magnitudes, and lower Si ii velocities.

In addition to a nearby envelope, both a violent merger in the DD scenario and the CD scenario may have material extending out to larger distances (Kashi & Soker 2011; Raskin & Kasen 2013; Hsiao et al. 2020). If that material is either launched in a wind or dynamically ejected at a constant velocity, then the extended material will have a r⁻² density profile (e.g., Moriya et al. 2023). That can be compared to the expected r⁻³ density profile of the nearby envelope (Piro & Morozova 2016). Studies have investigated the effects of shock heating the envelope and wind separately, but to our knowledge, no study has simultaneously simulated both. Piro & Morozova (2016), Maeda et al. (2023) show that a nearby envelope with an r⁻³ density profile is expected to produce a distinct bump in the early time light curves whereas Moriya et al. (2023) show that a diffuse, r⁻² wind may provide persistent additional UV luminosity through the maximum light. Qualitatively, the combination of these two effects may reproduce the observed 2003fg-like and 2002es-like light curves with their observed rising light-curve bumps and persistent blue UV colors through the maximum light. A combined envelope and wind-driven circumstellar medium may produce a correlation between the size of the ∼2 days rising light-curve bump or the UV luminosity and the combined pEW of the C i and C ii features at early times. Future theoretical and observational work is needed to test these qualitative considerations.

Finally, determining if 2003fg-like SNe Ia originate from the DD or CD scenario is another important open question. There are several predicted observational differences between the DD and CD scenarios. First, the DD scenario is predicted to show [O i] emission during the nebular phase (Pakmor et al. 2012), which may arise from low-velocity, asymmetric oxygen distributions caused by incomplete burning during a violent merger (Mazzali et al. 2022), whereas the CD scenario does not predict [O i] emission. Second, a violent merger in the DD scenario is predicted to be aspherical (Bulla et al. 2016); currently, no CD models offer predictions about polarization, but intuitively, one could expect these explosions to be spherical. Third and finally, the CD model of Lu et al. (2021) predicts a high X-ray flux due to a fast-receding photosphere and low opacity. This X-ray flux is as of yet undetected in any SN Ia to date (Lu et al. 2021), and future X-ray studies of 2002fg-like and 2003fg-like SNe Ia are also needed.

Foley et al. (2012) report A_V = 0.01 ± 0.01 mag for the host-galaxy of SN 2009ig and t_B ^max on MJD 55080.04. The Milky Way extinction is E(B − V)_MW = 0.03 mag (Schlafly & Finkbeiner 2011).

Foley et al. (2012) reported early time observations of SN 2009ig, a normal SN Ia. After subtracting a Arnett (1982) f ∝ t² fireball model, SN 2009ig has positive residuals, which are indicative of excess flux above what is expected with the fireball model. However, Foley et al. (2012) found the rise was well fit with a single-component power law. Given this acceptable single-component fit, we categorize SN 2009ig as an SN Ia without early time excess flux (i.e., as a single SN Ia). This determination is similar to that from Jiang et al. (2018), who also categorize SN 2009ig as having no early excess in either the UV or the optical.

Pereira et al. (2013) report t_B ^max on MJD 55814.51 and a host-galaxy extinction of E(B − V) = 0.03 ± 0.04 mag. The Milky Way extinction is E(B − V)_MW = 0.01 mag (Schlafly & Finkbeiner 2011).

SN 2011fe was an incredibly nearby normal SN Ia (Nugent et al. 2011). Located in M101 (NGC 5457) at 6.4 Mpc (Shappee & Stanek 2011), SN 2011fe is one of the most nearby SN Ia to date. As such, extensive searches for companion interaction under the Kasen (2010) models have been performed, all yielding no evidence of companion interaction (Li et al. 2011; Brown et al. 2012; Röpke et al. 2012; Shappee et al. 2013b, 2017; Tucker et al. 2022a, 2022c) or even a surviving companion (Lundqvist et al. 2015), which are predicted to be overluminous (Shappee et al. 2013a). Given the large sample of early data indicating strong agreement with the fireball model, we categorize SN 2011fe as a single SN Ia.

SN 2012cg was initially reported by Silverman et al. (2012), and they found t_B ^max occurred on MJD = 56080.0, and E(B − V) = 0.18 mag. Marion et al. (2016) also studied SN 2012cg and found t_B ^max on MJD 56081.3. Finally, Munari et al. (2013) determined t_B ^max happened on MJD 56082.0. We elect to use the Marion et al. (2016) value for t_B ^max, which is consistent with the Munari et al. (2013) value. The Milky Way extinction is E(B − V)_MW = 0.02 mag (Schlafly & Finkbeiner 2011).

SN 2012cg was initially reported by Silverman et al. (2012). Subsequent studies found evidence for Marion et al. (2016) and against (Shappee et al. 2018) a companion interaction. Irrespective to the mechanism of the early time emission, it is clear that emission beyond the predicted f ∝ tⁿ fireball model was detected. Thus, we categorize SN 2012 in the double category.

Childress et al. (2013) presented the first study of SN 2012fr and derived t_B ^max on MJD 56243.0 and an upper limit of E(B − V) < 0.015 mag via the Na i D line. A later study by Contreras et al. (2018) found a similar t_B ^max on MJD 56242.6. Contreras et al. (2018) examined the host-galaxy extinction using both the Na i D line from different spectra compared to that from Childress et al. (2013) as well as high quality Carnegie Supernova Project II (Phillips et al. 2019) photometry. This analysis by Contreras et al. (2018) resulted in a final E(B − V) = 0.03 ± 0.03 mag. We use the values from Contreras et al. (2018) in our analysis. The Milky Way extinction is E(B − V)_MW = 0.02 mag (Schlafly & Finkbeiner 2011).

There is a similarity between SN 2012fr and SN 2014J shown in Contreras et al. (2018), which suggests that the broken power law fitted to SN 2014J by Zheng et al. (2014) matches the data of SN 2012fr well. We categorize SN 2012fr as a double SN Ia, which is different than the categorization of Jiang et al. (2018), who categorize SN 2012fr as having no excess. Our determination is based on information provided in Contreras et al. (2018), which Jiang et al. (2018) may not have had available.

Yamanaka et al. (2014) found t_B ^max to be on MJD 56295.6, and they claim host-galaxy extinction is negligible. We accept their claim as valid given the presented B − V color curve in their Figure 1, as well as the lack of visible Na i D in their spectra. However, a negligible extinction in the optical will be larger in the UV, so we assume a host-galaxy extinction of A_V = 0.01 ± 0.01 mag to extrapolate to the Swift UV filters. The Milky Way line-of-sight extinction from Schlafly & Finkbeiner (2011) is E(B − V)_MW = 0.02 mag.

Yamanaka et al. (2014) present a smooth, single-component rise, so we categorize SN 2012ht as a single SN Ia, similarly to Jiang et al. (2018).

Scalzo et al. (2014) find ${t}_{B}^{\max }$ on MJD 56252.5 and a host-galaxy extinction of E(B − V)_HG = 0.02 ± 0.08 from the Lira et al. (1998) law. Using SNooPy, they find E(B − V)_HG = 0.01 ± 0.01, with R_V = 1.66 ± 1.66. We opt to use the extinction from the Lira et al. (1998) law assuming an R_V = 3.1. The Milky Way extinction is E(B − V)_MW = 0.02 mag (Schlafly & Finkbeiner 2011).

Scalzo et al. (2014) fit a two-component (Arnett 1982) with a shock component model to the bolometric light curve of LSQ12gdj. Thus, we categorize LSQ12gdj as a double SN Ia.

Zheng et al. (2013) derive t_B ^max to be on MJD 56500.7 and a host-galaxy extinction from fitting the Na i D line (Poznanski et al. 2012) to be E(B − V) = 0.15 mag. The Milky Way extinction is E(B − V)_MW = 0.13 mag (Schlafly & Finkbeiner 2011).

Zheng et al. (2013) found the best fit to the early time light curve of SN 2013dy was a broken power law. Thus, we categorize SN 2013dy as a double SN Ia. In their work, Jiang et al. (2018) also classify SN 2013dy as an early excess SN Ia.

Holmbo et al. (2019) present the discovery and an analysis of SN 2013gy where they find E(B − V)_HG = 0.11 ± 0.06 mag and t_B ^max on MJD 56648.5 from SNooPy (Burns et al. 2011, 2014) fits. The Schlafly & Finkbeiner (2011) Milky Way extinction toward SN 2013gy is E(B − V)_MW = 0.05 mag.

A single power-law rise fits the early time light curve of SN 2013gy (Holmbo et al. 2019), so we categorize it as a single SN Ia.

iPTF13dge was studied by Ferretti et al. (2016) who found t_B ^max occurred on MJD 56558.0. Ferretti et al. (2016) determined there was minimal host-galaxy toward iPTF13dge. They derived a value of E(B − V)_HG = 0.03 ± 0.04 mag. The Milky Way extinction for SN 2013gh is E(B − V)_MW = 0.08 mag (Schlafly & Finkbeiner 2011).

In their analysis, Ferretti et al. (2016) did not include fits to the early time light curve; however, we find no evidence for a two-component power-law rise; hence, we categorize iPTF13dge as a single SN Ia.

Hsiao et al. (2015) fit iPTF13ebh with SNooPY and fit t_B ^max on MJD 56622.9, and E(B − V)_HG = 0.05 ± 0.02 mag. The Milky Way extinction is E(B − V)_MW = 0.07 mag (Schlafly & Finkbeiner 2011).

While Hsiao et al. (2015) did not directly fit the early time rise of iPTF13ebh, a single-component power-law fit is a reasonable conclusion from their comparison to normal and 1991bg-like models. Thus, like Jiang et al. (2018), we categorize iPTF13ebh as a single SN Ia.

SNooPY fits performed by Shappee et al. (2016) show that the B-band maximum t_B ^max of ASASSN-14lp was on MJD 57015.3 and had a host-galaxy extinction of E(B − V)_HG = 0.33 ± 0.06 mag. The fits performed by Shappee et al. (2016) find that ASASSN-14lp is in good agreement with a single-component power-law early time light-curve rise. The Milky Way extinction is E(B − V)_MW = 0.02 mag (Schlafly & Finkbeiner 2011).

Determinations for the t_B ^max and E(B − V)_HG for iPTF14atg come from two different sources. First, Cao et al. (2015) determine that t_B ^max of iPTF14atg occurred on MJD 56799.2, but they do not provide an estimate for the host-galaxy extinction in their manuscript. Second, Kromer et al. (2016) determine the host-galaxy extinction for iPTF14atg is A_B = 0.00 ± 0.02 mag based on the Na i D line. We adopt a slightly different value of A_V = 0.01 ± 0.02 mag, which is consistent with the Kromer et al. (2015) value but is in the same band as all the other SNe Ia in our sample. The Milky Way extinction is E(B − V)_MW = 0.01 mag (Schlafly & Finkbeiner 2011).

Cao et al. (2015), Kromer et al. (2016) report early time light-curve bumps; thus, we classify iPTF14atg as a bump SNe Ia.

Smitka et al. (2015) find no evidence of extinction in the spectra of iPTF14bdn; thus, we assume A_V = 0.01 ± 0.01 mag. t_B ^max is on MJD 56822.5 (Smitka et al. 2015). The Milky Way extinction is E(B − V)_MW = 0.01 mag (Schlafly & Finkbeiner 2011).

While the early time Swift photometry in Smitka et al. (2015) may have an early time bump, we found no bump after redoing the photometry. Thus, we categorize iPTF14bdn as double SN Ia.

We adopt t_B ^max from Foley et al. (2014), which is MJD 56690.0. Unfortunately, determining the host-galaxy extinction is not so straightforward.

SN 2014J is one of the most heavily extincted SNe Ia to date. As such, there are a plethora of estimates on the host-galaxy extinction for this object. Amanullah et al. (2014) perform various extinction fits to their data. Their power-law fit $\left(\displaystyle \frac{{A}_{\lambda }}{{A}_{V}}={\left(\tfrac{\lambda }{{\lambda }_{V}}\right)}^{p}\right)$ yielded A_V = 1.85 ± 0.11 mag, whereas their Milky Way-like fit based on the Fitzpatrick (1999) parameterization yielded E(B − V) = 1.37 ± 0.03 mag, with R_V = 1.4 ± 0.1. Alternatively, Ashall et al. (2014) determine the host-galaxy extinction via selecting the A_V and R_V values, which optimize their abundance tomography models. This yields E(B − V) = 1.2 mag, and R_V = 1.38. Goobar et al. (2014) present two extinction values, one from SNooPy fits and the other based on the Phillips et al. (2013) method. The SNooPy fits yield E(B − V) = 1.22 ± 0.05 mag, with R_V = 1.4 ± 0.15, and the Phillips et al. (2013) method yields A_V = 2.5 ± 1.3 mag. Finally, Foley et al. (2014) presents several further calculations of A_V for SN 2014J. First, by using distant independent optical-infrared colors, they derive A_V = 1.95 ± 0.09 mag. Second, using the Phillips et al. (2013) relation, they derive A_V = 1.8 ± 0.9 mag from their high-resolution spectrum. Finally, using the color excess method, they derive A_V = 1.91 mag using a Fitzpatrick (1999) parameterization, and A_V = 1.82 mag using a Cardelli et al. (1989) parameterization. We elect to adopt the Foley et al. (2014) value measured by the high-resolution spectrum, which is also consistent with their color excess fits as well as the power-law model from Amanullah et al. (2014). Specifically, we take the value to be 1.8 ± 0.9 mag.

Siverd et al. (2015) find peak light on MJD 56690.62 using data from the Kilodegree Extremely Little Telescope North (Pepper et al. 2007; Siverd et al. 2012).

Zheng et al. (2014) demonstrate a two-component power-law fit to the early time light-curve rise, and Goobar et al. (2015) also found that multiple components better fit the rising light curve. Thus, we categorize SN 2014J as a double SN Ia. Unfortunately, the extinction is so severe in the UV that SN 2014J is not comparable in the UV to other SNe Ia; thus, we do not include it in plots and only include this discussion for completeness of the early time SN Ia sample.

Using MLCS2k2 (Jha et al. 2007), Im et al. (2015) find E(B − V)_hg = 0.04 ± 0.03 mag and t_B ^max on MJD 57105.98. Cartier et al. (2017) estimate the t_B ^max to be MJD 57106.5. Using the optical and NIR colors, they calculate various E(B − V) values, the weighted average of which they calculate to be E(B − V)_HG = 0.09 ± 0.02 mag. Their individual E(B − V) calculations use both the optical (Phillips et al. 1999) and NIR (Krisciunas et al. 2004a, 2004b) colors. The Milky Way extinction is E(B − V)_MW = 0.17 mag (Schlafly & Finkbeiner 2011).

Im et al. (2015) fit both single and double power laws to the early time data of SN 2015F and find that the single-component power law gives the best fit and that the double power-law fit converges to the single power-law result. Thus, we categorize SN 2015F as a single SN Ia, which is consistent with the categorization of Jiang et al. (2018).

Li et al. (2022) determined t_B ^max was on MJD 57084.1. By performing fits using the SALT2 modeling program (Guy et al. 2007), Li et al. (2022) calculate E(B − V)_HG = 0.15 ± 0.07 mag. The Milky Way extinction is E(B − V)_MW = 0.01 mag (Schlafly & Finkbeiner 2011).

An early time flux excess is claimed by Li et al. (2022). Their data show SN 2015bq has early time flux, which is greater than the normal SNe Ia they compare to. While the data are not early enough to be fit by power-law rises, we still opt to categorize SN 2015bq as a double SN Ia. Because SN 2015bq lacks Swift detections in the critical UVM2 band, we do not include it in our analysis, but we mention it here for completeness.

Ferretti et al. (2017) find a value of MJD 57498.8 for t_B ^max and A_V = 0.1 ± 0.2 mag from fitting the SED of SN 2011fe to the iPTF16abc data. Using SALT2, they find A_V = − 0.03 ± 0.04 mag. Despite finding deep Na i D lines, Ferretti et al. (2017) find weak reddening in the photometry of iPTF16abc. Dhawan et al. (2018) fit iPTF16abc using SNooPy and find E(B − V)_HG = 0.07 ± 0.02 mag, and R_V = 3.1. Finally, Miller et al. (2018) adopt E(B − V)_HG = 0.05 mag from Ferretti et al. (2017) and determine ${t}_{B}^{\max }$ occurred on MJD 57499.5. We adopt the values from Ferretti et al. (2017). Finally, the Milky Way extinction from Schlafly & Finkbeiner (2011) is E(B − V)_MW = 0.028 mag.

Miller et al. (2018) present early rise fits and find that a f ∝ t² model does not adequately describe the rising light curve of iPTF16abc whereas a nearly linear model fits the rise well. They did not fit a two-component power law, but given the single-component power law fits the rise well, we categorize iPTF16abc as a single SN Ia, which is different than the determination of Jiang et al. (2018).

The five papers on SN 2017cbv agree on both t_B ^max and host-galaxy extinction. First, Hosseinzadeh et al. (2017) find t_B ^max on MJD 57841.1 and negligible host-galaxy extinction due to the lack of Na i D absorption in their spectra. Second, Ferretti et al. (2017) find E(B − V) = 0.02 ± 0.01 mag from the Na i D line using the method of Poznanski et al. (2012). Third, Wee et al. (2018) determine t_B ^max to be on MJD 57840.4 and negligible host-galaxy extinction. Fourth, Wang et al. (2020) again find no significant host-galaxy extinction and a t_B ^max value of MJD 57840.4. Finally, Burke et al. (2022b) find no host-galaxy extinction and MJD 57840.3 as t_B ^max. For this work, we will use t_B ^max on MJD 57841.1 from Hosseinzadeh et al. (2017); and A_V = 0.06 ± 0.03 mag from Ferretti et al. (2017; assuming R_V = 3.1). The Milky Way extinction from Schlafly & Finkbeiner (2011) is E(B − V)_MW = 0.15 mag.

Hosseinzadeh et al. (2017), Burke et al. (2022b) show SN 2017cbv is fit better by multiple component models, and Jiang et al. (2018) categorize SN 2017cbv as an SN Ia with an early excess. Given that the light curve for SN 2017cbv monotonically increases in all the optical and UV bands, we place SN 2017cbv in our double category rather than the bump category.

Han et al. (2020) estimate A_V = 0.39 ± 0.03 mag from MLCS2k2 (Jha et al. 2007) fitting with an assumed R_V = 1.7. This R_V was presumably chosen by Han et al. (2020) to yield a peak B-band absolute magnitude of −19.2 mag. They also derive A_V = 1.34 ± 0.40 mag from the Na i D absorption line; however, they note that this large of an extinction value would make SN 2017cfd significantly brighter than most other SNe Ia at its t_B ^max on MJD 57843.4. The Milky Way extinction is E(B − V)_MW = 0.02 mag (Schlafly & Finkbeiner 2011). Finally, Han et al. (2020) show that SN 2017cfd is a normal SN Ia with a single power-law rise; thus, we categorize SN 2017cfd as a single SN Ia.

Burke et al. (2022b) find t_B ^max on MJD 57870.1 and negligible host-galaxy extinction. Thus, we assume a nominal host-galaxy extinction of A_V = 0.01 ± 0.01 mag. The Milky Way extinction is E(B − V)_MW = 0.22 mag (Schlafly & Finkbeiner 2011). Burke et al. (2022b) find no evidence of a two-component power-law rise. Thus, we categorize SN 2017cyy as a single SN Ia.

Brown et al. (2019) find MJD 57934.9 for t_B ^max as well as several values for the host-galaxy extinction, which they list in their Table 3. The methods Brown et al. (2019) use to estimate the host-galaxy extinction are the peak color, the Lira et al. (1998) law, Na i D fitting, and color excess from SNooPy and MLCS2k2 fits. Consistently, Burke et al. (2022b) find E(B − V) = 0.10 ± 0.01 mag and t_B ^max on MJD 57934.4 from SNooPy fits. We opt to combine the values from Brown et al. (2019) using a weighted average for our final extinction of A_V = 0.15 ± 0.04 mag. The Milky Way extinction is E(B − V)_MW = 0.09 mag (Schlafly & Finkbeiner 2011).

We categorize SN 2017erp as a single SN Ia despite the claim of companion interaction from Burke et al. (2022b). While they claim a two-component model fits the data better, the additional flux from the second component appears to only marginally improve the quality of the light-curve fit.

Three studies independently derive SN properties for SN 2017fgc. First, Zeng et al. (2021) also fit SN 2017fgc with SNooPy and find from the fits that t_B ^max was on MJD 57959.4 and that the host-galaxy extinction is E(B − V) = 0.17 ± 0.07 mag. Second, Burgaz et al. (2021) derive t_B ^max on MJD 57958.7 and adopt a host-galaxy extinction of E(B − V)_HG = 0.29 ± 0.02 mag from the Lira law Phillips et al. (1999). Finally, Burke et al. (2022b) fit SN 2017 with SNooPY and derived t_B ^max on MJD 57959.5, and a host-galaxy extinction of E(B − V) = 0.21 ± 0.01 mag. We adopt the values from Burke et al. (2022b) because their light curve is the most dense, and their data are solely from Las Cumbres Observatory Global Telescope observations (Brown et al. 2013), so S-corrections do not introduce an additional systematic uncertainty. The Milky Way extinction is A_V = 0.094 mag (Schlafly & Finkbeiner 2011).

We categorize SN 2017fgc as a single SN Ia based upon the fits performed by Zeng et al. (2021) and lack of companion signature from Burke et al. (2022b).

The three synoptic studies of ASASSN-18bt shortly after explosion (Dimitriadis et al. 2019; Li et al. 2019; Shappee et al. 2019) all used the t_B ^max and E(B − V)_HG derived by Li et al. (2019). Li et al. (2019) performed fits using SALT2, SNooPy, and MLCS2k2, which were all consistent. The values of their SNooPy fits are E(B − V)_HG = 0.00 ± 0.01 and t_B ^max on MJD 58162.7. We adopt their values but alter their E(B − V)_HG value to be 0.01 ± 0.01 such that we can extrapolate the small host-galaxy extinction into the UV. The Milky Way extinction is E(B − V)_MW = 0.04 mag (Schlafly & Finkbeiner 2011).

Shappee et al. (2019) showed the rising light curve of ASASSN-18bt was fit the best by a two-component power law, so we categorize ASASSN-18bt as a double SN Ia.

Both Yang et al. (2020), Burke et al. (2022b) agree that there is negligible optical host-galaxy extinction. While Burke et al. (2022b) does not provide an estimate for the host-galaxy-extinction, Yang et al. (2020) uses the "CMAGIC" technique to estimate E(B − V)_HG = 0.03 ± 0.03 mag, which we adopt. The Milky Way extinction is E(B − V)_MW = 0.05 mag (Schlafly & Finkbeiner 2011).

From fitting the light curves, Yang et al. (2020), Burke et al. (2022b) agree on t_B ^max as well, deriving t_B ^max on MJD 58149.7 and MJD 58149.6 respectively. We use the value from Yang et al. (2020).

Yang et al. (2020) found a single-component light-curve rise consistent with f ∝ t², and Burke et al. (2022b) also found a rise consistent with a fireball model. Thus, we categorize SN 2018gv as a single SN Ia.

From SNooPy fits, Burke et al. (2022b) determine E(B − V)_HG = 0.04 ± 0.01 mag and MJD 58183.9 for t_B ^max, as well as that SN 2018xx does not show a two-component rise. Thus, we categorize SN 2018xx as a single SN Ia. The Milky Way extinction is E(B − V)_MW = 0.09 mag (Schlafly & Finkbeiner 2011).

From SNooPy fits, Burke et al. (2022b) determine MJD 58183.3 for t_B ^max. Burke et al. (2022b) claim negligible host-galaxy extinction; thus, we adopt A_V = 0.01 ± 0.01 mag. The Milky Way extinction is E(B − V)_MW = 0.13 mag (Schlafly & Finkbeiner 2011).

While Burke et al. (2022b) claim an early excess flux from companion interaction in the rising light curve of SN 2018yu, the companion shock contribution to the early time light-curve rise is small, and neither Tucker et al. (2020) nor Graham et al. (2022) find evidence of Hα in the nebular spectra. Additionally, the companion flux contribution appears small, so the improvement to the fit is marginal. Thus, we categorize SN 2018yu as a single SN Ia.

Wang et al. (2021) determined ${t}_{B}^{\max }$ was on MJD 58203.8, and from the Na i D line relationship from Poznanski et al. (2012), they estimate E(B − V)_HG = 0.11 ± 0.05 mag. The Milky Way extinction is E(B − V)_MW = 0.03 mag (Schlafly & Finkbeiner 2011).

The early time light curve was fit best by a single power law by Wang et al. (2021) using Kepler data. Hence, we categorize SN 2018agk as a single SN Ia. SN 2018agk is distant (d > 100 Mpc), so the UV data are faint—there is only 1 detection in the UVM2 band, and it is barely above 3σ. SN 2018agk is included in the tables for completion but is not factored into our analysis.

Ni et al. (2022) found t_B ^max on MJD 58222.2 via a SNooPy fit and an upper limit for the host-galaxy extinction of E(B − V)_HG < 0.02 mag via fitting the Na i D line. Burke et al. (2022b) also performed SNooPy fits and derived MJD 58222.1 for t_B ^max and negligible host-galaxy extinction. We adopt the values from Ni et al. (2022). The Milky Way extinction is E(B − V)_MW = 0.07 mag (Schlafly & Finkbeiner 2011).

Burke et al. (2022b) find a single-component rise explains the early time light curve of SN 2018aoz, and Ni et al. (2022, 2023) find that, while reddened, SN 2018aoz is consistent with a single power-law rise. Thus, we categorize SN 2018aoz as a single SN Ia.

Burke et al. (2022b) used SNooPy to fit SN 2019np and found MJD 58509.6 to be t_B ^max. Sai et al. (2022) fit a polynomial to the light curve of SN 2019np and found t_B ^max on MJD 58510.2. From SNooPy fits and the Na i D absorption equivalent width, Sai et al. (2022) determine E(B − V)_HG = 0.10 ± 0.04 mag. The Milky Way extinction is E(B − V)_MW = 0.02 mag (Schlafly & Finkbeiner 2011).

Burke et al. (2022b) do not find signatures of companion interaction, which is consistent with the later work by Ni et al. (2022, 2023). However, Ni et al. (2023) finds that, while reddened at early times (Ni et al. 2022), SN 2019np has an early excess flux consistent with a multiple-power-law rise. Thus, we categorize SN 2019np as a double SN Ia.

Pellegrino et al. (2020) find t_B ^max on MJD 58619.5 from SALT2 fits, and they assume the host-galaxy extinction from Kawabata et al. (2020). Kawabata et al. (2020) determine t_B ^max on MJD 58618.2 from a polynomial fit to data around the maximum. We adopt the SALT2 fit result from Pellegrino et al. (2020) as our t_B ^max. The Milky Way extinction is E(B − V)_MW = 0.01 mag (Schlafly & Finkbeiner 2011).

They estimate the host-galaxy extinction from SNooPy fits, Phillips et al. (1999), Reindl et al. (2005) E(B − V) evolution relationships, and the Si ii λ 6355 and peak intrinsic E(B − V) color relationships from Foley et al. (2011), Blondin et al. (2012). Ultimately, they assume the SNooPy value, which we will also adopt. This value is E(B − V)_HG = 0.09 ± 0.06 mag, and R_V = 1.55, which corresponds to A_V = 0.14 ± 0.09 mag.

SN 2019ein does not show an early excess Kawabata et al. (2020), so we label it as a single SN Ia.

Both Miller et al. (2020), Burke et al. (2021) are in agreement on when t_B ^max occurred, with respective values of MJD 58863.3 and 58863.1. We adopt the mean value of MJD 58863.2 for t_B ^max.

With respect to host-galaxy extinction, Miller et al. (2020) used Na i D lines to find E(B − V)_HG ≈ 0.032 mag. Burke et al. (2021) found that light-curve fitting methods resulted in highly discordant estimates for the host-galaxy extinction. This is to be expected given how unique SN 2019yvq is. However, Burke et al. (2021) fit the Na i D line and found $E{(B-V)}_{\mathrm{HG}}={0.05}_{-0.03}^{+0.05}$ mag. This is consistent with the derived host-galaxy extinction from Miller et al. (2020). We adopt the Burke et al. (2021) host-galaxy extinction value. The Milky Way extinction is E(B − V)_MW = 0.02 mag (Schlafly & Finkbeiner 2011).

Miller et al. (2020), Siebert et al. (2020), Burke et al. (2021), and Tucker et al. (2021) all present analyses of the early time bump of SN 2019yvq. We classify SN 2019yvq as a bump Ia.

Jiang et al. (2021) suggest negligible host-galaxy extinction from a lack of Na i D absorption in their spectra as well as a large distance from the center of the host-galaxy and a t_B ^max of MJD 58979.3 from a polynomial fit to the data near peak. We adopt their values, assuming A_V = 0.01 ± 0.01 mag. The Milky Way extinction is E(B − V)_MW = 0.04 mag (Schlafly & Finkbeiner 2011).

The data presented by Jiang et al. (2021) show a clear early bump for SN 2020hvf; thus, we categorize it as a bump SN Ia.

Sand et al. (2021) fit a fourth-order polynomial to the data near peak and perform 1000 resamples based on the photometric uncertainties. They find negligible host-galaxy extinction based on the Phillips et al. (1999) relationship and MJD 59041.8 as t_B ^max. We adopt their value for t_B ^max and assume A_V = 0.01 ± 0.01 mag. The Milky Way extinction is E(B − V)_MW = 0.03 mag (Schlafly & Finkbeiner 2011).

There are early time data available for SN 2020nlb; however, Sand et al. (2021) does not fit the early time light curve. We perform a Markov Chain Monte Carlo fit using emcee (Foreman-Mackey et al. 2013) to the rising light curve and find it is consistent with a single-power-law rise. Thus, we categorize SN 2020nlb as a single SN Ia.

Fausnaugh et al. (2023) present TESS observations of SN 2020tld. The TESS data do not cover the light-curve peak. Since their observations are only in one band and they have no spectra, the host-galaxy extinction is uncertain. However, SN 2020tld lies well outside its host, so we assume A_V = 0.01 ± 0.01 mag. Finally, the rising light-curve fits from Fausnaugh et al. (2023) disfavor companion interaction, so we categorize SN 2020tld as a single SN Ia. There are no preexplosion images, nor postexplosion templates in Swift for SN 2020tld, so we do not include it in our figures or analysis. We mention it here for completeness.

Maguire et al. (2023) found a g-band maximum light on MJD 59131.0, which we adopt as t_B ^max. t_B ^max and t_g ^max are close enough that this assumption will not significantly impact any of our results. Since they do not observe any Na i D absorption in their spectra, Maguire et al. (2023) claim negligible host-galaxy extinction. Thus, we assume A_V = 0.01 ± 0.01 mag for SN 2020udy. The Milky Way extinction is E(B − V)_MW = 0.07 mag (Schlafly & Finkbeiner 2011). Finally, Maguire et al. (2023) fit a single power law to the early time light-curve rise; thus, we categorize SN 2020udy as a single SN Ia. Unfortunately, SN 2020udy lacks preexplosion imaging, so we exclude it from our analysis because the photometry would not be host subtracted.

DerKacy et al. (2023) fit the light curves of SN 2021fxy with SNooPy. From these fits, they find t_B ^max on MJD 59305.1 and a small host-galaxy extinction of E(B − V)_HG = 0.02 ± 0.06 mag. We adopt these values, along with a Milky Way extinction of E(B − V)_MW = 0.08 mag (Schlafly & Finkbeiner 2011). The light curves presented by DerKacy et al. (2023) are consistent with a single-component rise, so we categorize SN 2021fxy as a single SN Ia.

Zhang et al. (2022) fit the light-curve peak with a second-order polynomial and determine t_B ^max was on MJD 59321.9. They posit negligible host-galaxy extinction. Ward et al. (2023) fit SN 2021hpr using the BayeSN fitting program (Thorp et al. 2021; Mandel et al. 2022). They find t_B ^max on MJD 59321.4. Their Bayesian framework enables fitting with a fixed R_V and with a uniform prior between 1 and 6. With R_V fixed at 2.66, they find A_V = 0.27 ± 0.04 mag; with R_V drawn from a uniform prior distribution ${ \mathcal U }(1,6)$, they find A_V = 0.28 ± 0.07 mag. Finally, Lim et al. (2023) use the Phillips et al. (1999) relationship to estimate the host-galaxy extinction, which yields an estimate of E(B − V)_HG = 0.08 ± 0.04 mag. For t_B ^max, they find that the light curve peaked on MJD 59321.7. We adopt the values from Ward et al. (2023). The Milky Way extinction is E(B − V)_MW = 0.02 mag (Schlafly & Finkbeiner 2011).

Lim et al. (2023) found a two-component best fit SN 2021hpr; thus, we categorize it as a double SN Ia.

Dimitriadis et al. (2023) found that SN 2021zny peaked on MJD 59498.4 by fitting the light curve near peak with a polynomial. Using the Na i D line and the Poznanski et al. (2012) relationship, they derive E(B − V)_HG = 0.10 ± 0.07 mag. We adopt both of their values for this work. The Milky Way extinction is E(B − V)_MW = 0.04 mag (Schlafly & Finkbeiner 2011).

TESS observed SN 2021zny, and the rising TESS light curve shows a small bump (Dimitriadis et al. 2023; Fausnaugh et al. 2023). However, Fausnaugh et al. (2023) express some concerns over the veracity of this bump. They note similar light-curve variations at the light-curve peak. Furthermore, they note that SN 2021zny is on a CCD strap, which should produce noise similar to the observed peak variations. Their light-curve fits disfavor companion interaction, so this is an argument against an astrophysical origin for the bump. We categorize SN 2021zny as a bump Ia with the caveats noted by Fausnaugh et al. (2023).

Ashall et al. (2022) find t_B ^max on MJD 59547.2 and do not provide a host-galaxy extinction value. Hosseinzadeh et al. (2022) find MJD 59546.5 as t_B ^max using a polynomial fit to the data near peak. They use their high-resolution spectrum to determine host-galaxy extinction from the Na i D line using the method of Poznanski et al. (2012). They find E(B − V)_HG = 0.10 mag. Using the Phillips et al. (1999) relationship, they find E(B − V)_HG = 0.04 mag, which is consistent with their Na i D-derived value. We adopt the values from Hosseinzadeh et al. (2022) for both t_B ^max and A_V ; specifically, A_V = 0.31 mag from the Na i D line. The Milky Way extinction is E(B − V)_MW = 0.01 mag (Schlafly & Finkbeiner 2011).

Both Ashall et al. (2022), Hosseinzadeh et al. (2022) find a two-component light-curve fit to SN 2021aefx. Thus, we categorize SN 2021aefx as a double SN Ia.

Fausnaugh et al. (2023) present TESS observations of SN 2022eyw; however, the TESS sector only covers the rising light curve and not the peak. Since their observations are only in one band, we adopt an extinction of A_V = 0.02 ± 0.05 mag, motivated by the lack of Na i D in the TNS spectra, but the position is in the host-galaxy, so there may be some extinction. The Milky Way extinction is E(B − V)_MW = 0.01 mag (Schlafly & Finkbeiner 2011).

The rising light-curve fits from Fausnaugh et al. (2023) disfavor companion interaction, so we categorize SN 2022eyw as a single SN Ia. There are no preexplosion images, nor postexplosion templates in Swift for SN 2022eyw, so we do not include it in our figures or analysis. We mention it here for completeness.

Srivastav et al. (2023b) searched for a host-galaxy; however, they did not satisfactorily locate a clear host-galaxy candidate. Because there is no sign of a host-galaxy or Na i D lines, we conclude that there is negligible host-galaxy extinction. In line with other SNe Ia in our sample with negligible host-galaxy extinction, we assume A_V = 0.01 ± 0.01 mag. While they do not clearly state the t_B ^max they derive, it can be inferred from other statements in the paper to be on MJD ∼59707.5. The Milky Way extinction is E(B − V)_MW = 0.10 mag (Schlafly & Finkbeiner 2011).

SN 2022ilv shows an early time bump based on an ATLAS nondetection. Srivastav et al. (2023b) evaluate this nondetection and determine it is valid. We agree with their determination, and thus, we categorize SN 2022ilv as a bump SN Ia.

Both Wang et al. (2024), Hosseinzadeh et al. (2023) agree that host-galaxy extinction is negligible; thus, we adopt A_V = 0.01 ± 0.01 mag. For t_B ^max, we adopt MJD 59992.5 as our value, which is the average between the Wang et al. (2024), Hosseinzadeh et al. (2023) values of MJD 59992.6 and MJD 59992.4, respectively. The Milky Way extinction is E(B − V)_MW = 0.01 mag (Schlafly & Finkbeiner 2011).

SN 2023bee is the most recent SN with early time light-curve coverage. Both Wang et al. (2024), Hosseinzadeh et al. (2023) report early excess flux and two-component light curves. We categorize SN 2023bee as a double SN Ia.