Low-Luminosity Type IIP Supernovae from the Zwicky Transient Facility Census of the Local Universe. III: Hunting for electron-capture supernovae using nebular spectroscopy
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2026
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| author | Das, Kaustav K. Jerkstrand, Anders Kasliwal, Mansi M. Sollerman, Jesper Fremling, Christoffer Schulze, Steve Gal-Yam, Avishay Ahumada, Tomas Anand, Shreya van Baal, Bart Coughlin, Michael W. Covarrubias, Sofia Dekany, Richard Earley, Nicholas Jacobson-Galán, W. V. Jaimes, Joahan Castaneda Masci, Frank J. Qin, Yu-Jing Riddle, Reed Rose, Sam Sharma, Yashvi |
| author_facet | Das, Kaustav K. Jerkstrand, Anders Kasliwal, Mansi M. Sollerman, Jesper Fremling, Christoffer Schulze, Steve Gal-Yam, Avishay Ahumada, Tomas Anand, Shreya van Baal, Bart Coughlin, Michael W. Covarrubias, Sofia Dekany, Richard Earley, Nicholas Jacobson-Galán, W. V. Jaimes, Joahan Castaneda Masci, Frank J. Qin, Yu-Jing Riddle, Reed Rose, Sam Sharma, Yashvi |
| contents | Electron-capture supernovae (ECSNe) may arise from ONeMg-core collapse in super-asymptotic giant branch (sAGB) stars near the low-mass core-collapse limit ($\approx\!8$--$10$\,\Msun). At early times, models predict that ECSNe resemble low-mass red supergiant iron-core-collapse SNe (FeCCSNe), making the two channels difficult to distinguish. Nebular spectroscopy, however, can reveal differences in ejecta composition. We present a systematic sample of nebular spectra of 19 low-luminosity Type IIP (LLIIP) SNe from the ZTF CLU survey, obtained 115$-$450\,d after explosion. Their low velocities expose narrow lines blended in brighter SNe, which we identify and model to constrain progenitor properties. We find a strong correlation between the FWHM of H\,\textsc{i}\,$λ$6563 and peak luminosity, showing that LLIIP SNe occupy the low-energy end of the core-collapse population, but no correlation with plateau duration, suggesting that envelope and core properties are not tightly linked. Only one SN reaches the extremely low H\,\textsc{i}\,$λ$6563 widths predicted for the weakest $\sim$9\,M$_\odot$ explosion models, implying that such low-energy events are intrinsically rare. Combining our sample with 118 literature nebular spectra of Type II SNe, we infer an IMF slope of $2.1\pm1.2$. We also introduce an `ECSN score'' based on the absence of He- and O-shell emission lines, and identify two plausible ECSN candidates, SN~2023bvj and SN~2024btj. However, neither shows the extremely narrow nebular lines predicted by current ECSN models. If ECSNe arise predominantly through the LLIIP channel, we infer an upper limit on the ECSN rate of $\lesssim (5$--$8)\times10^{2}\,\mathrm{Gpc^{-3}\,yr^{-1}}$, corresponding to a narrow sAGB progenitor mass window of $ΔM_{\rm sAGB} \lesssim 0.02$--$0.06\,\mathrm{M_\odot}$. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2605_18960 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Low-Luminosity Type IIP Supernovae from the Zwicky Transient Facility Census of the Local Universe. III: Hunting for electron-capture supernovae using nebular spectroscopy Das, Kaustav K. Jerkstrand, Anders Kasliwal, Mansi M. Sollerman, Jesper Fremling, Christoffer Schulze, Steve Gal-Yam, Avishay Ahumada, Tomas Anand, Shreya van Baal, Bart Coughlin, Michael W. Covarrubias, Sofia Dekany, Richard Earley, Nicholas Jacobson-Galán, W. V. Jaimes, Joahan Castaneda Masci, Frank J. Qin, Yu-Jing Riddle, Reed Rose, Sam Sharma, Yashvi High Energy Astrophysical Phenomena Electron-capture supernovae (ECSNe) may arise from ONeMg-core collapse in super-asymptotic giant branch (sAGB) stars near the low-mass core-collapse limit ($\approx\!8$--$10$\,\Msun). At early times, models predict that ECSNe resemble low-mass red supergiant iron-core-collapse SNe (FeCCSNe), making the two channels difficult to distinguish. Nebular spectroscopy, however, can reveal differences in ejecta composition. We present a systematic sample of nebular spectra of 19 low-luminosity Type IIP (LLIIP) SNe from the ZTF CLU survey, obtained 115$-$450\,d after explosion. Their low velocities expose narrow lines blended in brighter SNe, which we identify and model to constrain progenitor properties. We find a strong correlation between the FWHM of H\,\textsc{i}\,$λ$6563 and peak luminosity, showing that LLIIP SNe occupy the low-energy end of the core-collapse population, but no correlation with plateau duration, suggesting that envelope and core properties are not tightly linked. Only one SN reaches the extremely low H\,\textsc{i}\,$λ$6563 widths predicted for the weakest $\sim$9\,M$_\odot$ explosion models, implying that such low-energy events are intrinsically rare. Combining our sample with 118 literature nebular spectra of Type II SNe, we infer an IMF slope of $2.1\pm1.2$. We also introduce an `ECSN score'' based on the absence of He- and O-shell emission lines, and identify two plausible ECSN candidates, SN~2023bvj and SN~2024btj. However, neither shows the extremely narrow nebular lines predicted by current ECSN models. If ECSNe arise predominantly through the LLIIP channel, we infer an upper limit on the ECSN rate of $\lesssim (5$--$8)\times10^{2}\,\mathrm{Gpc^{-3}\,yr^{-1}}$, corresponding to a narrow sAGB progenitor mass window of $ΔM_{\rm sAGB} \lesssim 0.02$--$0.06\,\mathrm{M_\odot}$. |
| title | Low-Luminosity Type IIP Supernovae from the Zwicky Transient Facility Census of the Local Universe. III: Hunting for electron-capture supernovae using nebular spectroscopy |
| topic | High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2605.18960 |