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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. 

We present a comparative study of two nearby type Ia supernovae (SNe Ia), 2018xx and 2019gbx, that exploded in NGC 4767 and MCG-02-33-017 at a distance of 48 Mpc and 60 Mpc, respectively. The B -band light curve decline rate for SN 2018xx is estimated to be 1.48 ± 0.07 mag and for SN 2019gbx it is 1.37 ± 0.07 mag. Despite the similarities in photometric evolution, quasi-bolometric luminosity, and spectroscopy between these two SNe Ia, SN 2018xx has been found to be fainter by about ∼0.38 mag in the B -band and has a lower 56 Ni yield. Their host galaxies have similar metallicities at the SN location, indicating that the differences between these two SNe Ia may be associated with the higher progenitor metallicity of SN 2018xx. Further inspection of the near-maximum-light spectra has revealed that SN 2018xx has relatively strong absorption features near 4300 Å relative to SN 2019gbx. The application of the code TARDIS fitting to the above features indicates that the absorption features near 4300 Å appear to be related to not only Fe  II /Mg  II abundance but possibly to the other element abundances as well. Moreover, SN 2018xx shows a weaker carbon absorption at earlier times, which is also consistent with higher ejecta metallicity. 

Abstract Dust associated with various stellar sources in galaxies at all cosmic epochs remains a controversial topic, particularly whether supernovae play an important role in dust production. We report evidence of dust formation in the cold, dense shell behind the ejecta–circumstellar medium (CSM) interaction in the Type Ia-CSM supernova (SN) 2018evt three years after the explosion, characterized by a rise in mid-infrared emission accompanied by an accelerated decline in the optical radiation of the SN. Such a dust-formation picture is also corroborated by the concurrent evolution of the profiles of the Hα emission line. Our model suggests enhanced CSM dust concentration at increasing distances from the SN as compared to what can be expected from the density profile of the mass loss from a steady stellar wind. By the time of the last mid-infrared observations at day +1,041, a total amount of 1.2 ± 0.2 × 10⁻² M_⊙of new dust has been formed by SN 2018evt, making SN 2018evt one of the most prolific dust factories among supernovae with evidence of dust formation. The unprecedented witness of the intense production procedure of dust may shed light on the perceptions of dust formation in cosmic history. 

Abstract We present high-cadence photometric and spectroscopic observations of supernova (SN) 2024ggi, a Type II SN with flash spectroscopy features, which exploded in the nearby galaxy NGC 3621 at ∼7 Mpc. The light-curve evolution over the first 30 hr can be fit by two power-law indices with a break after 22 hr, rising fromM_V≈ −12.95 mag at +0.66 day toM_V≈ −17.91 mag after 7 days. In addition, the densely sampled color curve shows a strong blueward evolution over the first few days and then behaves as a normal SN II with a redward evolution as the ejecta cool. Such deviations could be due to interaction with circumstellar material (CSM). Early high- and low-resolution spectra clearly show high-ionization flash features from the first spectrum to +3.42 days after the explosion. From the high-resolution spectra, we calculate the CSM velocity to be 37 ± 4 km s⁻¹. We also see the line strength evolve rapidly from 1.22 to 1.49 days in the earliest high-resolution spectra. Comparison of the low-resolution spectra with CMFGEN models suggests that the pre-explosion mass-loss rate of SN 2024ggi falls in the range of 10⁻³–10⁻²M_☉yr⁻¹, which is similar to that derived for SN 2023ixf. However, the rapid temporal evolution of the narrow lines in the spectra of SN 2024ggi (R_CSM∼ 2.7 × 10¹⁴cm) could indicate a smaller spatial extent of the CSM than in SN 2023ixf (R_CSM∼ 5.4 × 10¹⁴cm), which in turn implies a lower total CSM mass for SN 2024ggi. 

Photometry shown in Figure Extended Data 4 (a) of Wang, Lingzhi, et al. 2024, Nature Astronomy, https://doi.org/10.1038/s41550-024-02197-9.Phase is days since B-band maximum MJD 58352.BVgri-band photometry from 1-m network at Las Cumbres Observatory.SN2018evt_lcogt_lc.datBVgri-band photometry from 2.4-m LiJiang Telescope (LJT) and 60/90-cm XingLong Schmidt Telescope (XLST)SN2018evt_xlt_ljt_lc.datOptical and NIR spectra data shown in Figures Extended Data 2, 3, and Table Extended Data 2 of Wang, Lingzhi, et al. 2024, Nature Astronomy, NIR spectraSN2018evt_181224_spex.txt SN2018evt_190511_spex.txtSN2018evt_190617_spex.txtSN2018evt_200119_spex.txtSN2018evt_20190101_gnirs.txtSN2018evt_20190108_gnirs.txtSN2018evt_20190516_fire.datSN2018evt_20190712_fire.datOptical spectraOptical spectra observed with 2.4-m LiJiang Telescope (LJT)SN2018evt_190104_LJT_G3.datSN2018evt_190131_LJT_G3.datSN2018evt_190328_LJT_G3.datSN2018evt_190520_LJT_G3.datOptical spectra observed with 2.16-m XingLong Telescope (XLT)SN2018evt_20190208_2458551.3570_bao_bfosc.txtSN2018evt_20190220_2458563.3588_bao-bfosc.txtSN2018evt_20190413_2458587.2169_bao-bfosc.txtOptical spectra observed with 3.6-m ESO New Technology Telescope (NTT)SN2018evt_20180812_NTT_Gr13_Free_slit1.0_58346_1_e.asciSN2018evt_20190425_NTT_Gr13_Free_slit1.0_58599_1_e.asciSN2018evt_20190512_NTT_Gr13_Free_slit1.0_58616_1_e.asciSN2018evt_20190608_NTT_Gr13_Free_slit1.0_58643_1_e.asciSN2018evt_20200218_NTT_Gr13_Free_slit1.0_58899_1_e.asciSN2018evt_20200322_NTT_Gr13_Free_slit1.0_58931_1_e.asciOptical spectrum observed with WiFes mounted on 2.3-m telescope at the Siding Spring Observatory (WiFeS)SN2018evt_20190624_ANU_Wifes.datOptical spectrum observed with 2.0-m Faulkes Telescope North (FTN)/FLOYDSSN2018evt_20191224_FTN-floyds-redblu_145742.306.asciiSN2018evt_20200119_FTN-floyds-redblu_133856.906.asciiSN2018evt_20200203_FTN-floyds-redblu_125905.990.ascii 

Abstract We present a high-cadence short term photometric and spectroscopic monitoring campaign of a type Ibn SN 2019wep, which is one of the rare SN Ibn after SNe 2010al and 2019uo to display signatures of flash ionization (He ii , C iii , N iii ). We compare the decline rates and rise time of SN 2019wep with other SNe Ibn and fast transients. The post-peak decline in all bands (0.1 mag day −1 ) are consistent with SNe Ibn but less than the fast transients. On the other hand, the Δ m 15 values are slightly lower than the average values for SNe Ibn but consistent with the fast transients. The rise time is typically shorter than SNe Ibn but longer than fast transients. SN 2019wep lies at the fainter end of SNe Ibn but possesses an average luminosity among the fast transients sample. The peculiar color evolution places it between SNe Ib and the most extreme SNe Ibn. The bolometric light-curve modeling shows resemblance with SN 2019uo with ejecta masses consistent with SNe Ib. SN 2019wep belongs to the P cygni subclass of SNe Ibn and shows faster evolution in line velocities as compared to the emission subclass. The post-maximum spectra show close resemblance with ASASSN-15ed hinting it to be of SN Ib nature. The low He i CSM velocities and residual H α further justifies it and provide evidence of an intermittent progenitor between Wolf-Rayet and LBV stars.