SN 2021ukt: A Transitional Supernova with a Short Plateau and Persistent Interaction
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| Main Authors: | , , , , , , , , , , , , , , , , , , , , , , , |
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| Format: | Preprint |
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2025
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| _version_ | 1866911292060598272 |
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| author | Pichay, Neil R. Vasylyev, Sergiy S. Liddle, Audrey M. Filippenko, Alexei V. Zheng, WeiKang Brink, Thomas G. Yang, Yi Graham, Matthew Stern, Daniel Hiramatsu, Daichi Gutiérrez, Claudia P. Bostroem, K. Azalee Gonzalez, Estefania Padilla Howell, D. Andrew McCully, Curtis Newsome, Megan Pellegrino, Craig Terreran, Giacomo Altunin, Ivan Baer-Way, Raphael Chandler, Vidhi deGraw, Asia A. Jennings, Connor F. May, Michael B. |
| author_facet | Pichay, Neil R. Vasylyev, Sergiy S. Liddle, Audrey M. Filippenko, Alexei V. Zheng, WeiKang Brink, Thomas G. Yang, Yi Graham, Matthew Stern, Daniel Hiramatsu, Daichi Gutiérrez, Claudia P. Bostroem, K. Azalee Gonzalez, Estefania Padilla Howell, D. Andrew McCully, Curtis Newsome, Megan Pellegrino, Craig Terreran, Giacomo Altunin, Ivan Baer-Way, Raphael Chandler, Vidhi deGraw, Asia A. Jennings, Connor F. May, Michael B. |
| contents | We present spectroscopic and photometric observations of supernova (SN) 2021ukt, a peculiar short-plateau object that was originally identified as a Type IIn SN and later underwent an unprecedented transition to a Type Ib (possibly Type IIb) SN. The early-time light curves of SN 2021ukt exhibit a ~25 day plateau. Such a short phase of hydrogen recombination suggests a rather thin H-rich outer envelope of the progenitor star. The relatively narrow Balmer emission lines in spectra of SN 2021ukt during the first week indicate the interaction between the expanding ejecta and the immediate circumstellar material (CSM). This Hα line is observed throughout its helium-rich ejecta-dominated phase and nebular phase, suggesting persistent interaction with a radially extended CSM profile. We explore the synthetic light-curve model among grids of parameters generated by MESA+STELLA. We also compare the spectrophotometric evolution of SN 2021ukt with several well-sampled supernovae that exhibit a short plateau and persistent ejecta-CSM interaction. An estimate of the progenitor mass of SN 2021ukt is made based on the flux ratio between [Ca II] λλ 7291, 7324 and [O I] λλ 6300, 6364 during its nebular phase. Our analysis suggests that the progenitor star of SN 2021ukt has a zero-age main-sequence (ZAMS) mass of about 12 solar masses, a mass of radioactive nickel-56 synthesized in the SN ejecta of about 0.04 solar masses, and a mass of the H-rich envelope of about 0.5 solar masses. This study adds to the growing sample of transitional supernovae, reinforcing evidence for a continuum of underrepresented progenitors whose evolutionary pathways lie between those of standard SN models. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2511_22923 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | SN 2021ukt: A Transitional Supernova with a Short Plateau and Persistent Interaction Pichay, Neil R. Vasylyev, Sergiy S. Liddle, Audrey M. Filippenko, Alexei V. Zheng, WeiKang Brink, Thomas G. Yang, Yi Graham, Matthew Stern, Daniel Hiramatsu, Daichi Gutiérrez, Claudia P. Bostroem, K. Azalee Gonzalez, Estefania Padilla Howell, D. Andrew McCully, Curtis Newsome, Megan Pellegrino, Craig Terreran, Giacomo Altunin, Ivan Baer-Way, Raphael Chandler, Vidhi deGraw, Asia A. Jennings, Connor F. May, Michael B. Solar and Stellar Astrophysics High Energy Astrophysical Phenomena We present spectroscopic and photometric observations of supernova (SN) 2021ukt, a peculiar short-plateau object that was originally identified as a Type IIn SN and later underwent an unprecedented transition to a Type Ib (possibly Type IIb) SN. The early-time light curves of SN 2021ukt exhibit a ~25 day plateau. Such a short phase of hydrogen recombination suggests a rather thin H-rich outer envelope of the progenitor star. The relatively narrow Balmer emission lines in spectra of SN 2021ukt during the first week indicate the interaction between the expanding ejecta and the immediate circumstellar material (CSM). This Hα line is observed throughout its helium-rich ejecta-dominated phase and nebular phase, suggesting persistent interaction with a radially extended CSM profile. We explore the synthetic light-curve model among grids of parameters generated by MESA+STELLA. We also compare the spectrophotometric evolution of SN 2021ukt with several well-sampled supernovae that exhibit a short plateau and persistent ejecta-CSM interaction. An estimate of the progenitor mass of SN 2021ukt is made based on the flux ratio between [Ca II] λλ 7291, 7324 and [O I] λλ 6300, 6364 during its nebular phase. Our analysis suggests that the progenitor star of SN 2021ukt has a zero-age main-sequence (ZAMS) mass of about 12 solar masses, a mass of radioactive nickel-56 synthesized in the SN ejecta of about 0.04 solar masses, and a mass of the H-rich envelope of about 0.5 solar masses. This study adds to the growing sample of transitional supernovae, reinforcing evidence for a continuum of underrepresented progenitors whose evolutionary pathways lie between those of standard SN models. |
| title | SN 2021ukt: A Transitional Supernova with a Short Plateau and Persistent Interaction |
| topic | Solar and Stellar Astrophysics High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2511.22923 |