A prolonged plateau-to-tail transition in the Type II supernova SN 2025abyc
- 1Yunnan Observatories, Chinese Academy of Sciences
- 2Department of Astronomy, School of Physics and Technology, Wuhan University
Abstract
We present optical photometric and spectroscopic observations of the Type II supernova (SN) SN 2025abyc. During the optically thick phase, which occurs approximately 10 and 70 d after explosion, its light curves show strongly wavelength-dependent decline rates of approximately 2.7, 2.1, 0.9, and 0.8 mag (100 d)−1 in the g, c, r, and o bands, respectively. At approximately 70 d, the light curves begin to depart from their nearly linear plateau evolution and gradually transition towards the radioactive tail. A Fermi–Dirac fit to the well-sampled ATLAS o-band light curve yields a transition midpoint of tPT ≈ 100.5 d. The interval between the end of the linear plateau and this transition midpoint is approximately 30 d, indicating a prolonged plateau-to-tail transition. This timescale is comparable to those measured for SN 2013by, SN 2013ej, and SN 2014G. Spectroscopically, at +13 d post-explosion, the Hα profile appears weak and broad, whereas Hβ and Hγ display clear P-Cygni profiles. This morphology can be explained by the normal early spectroscopic evolution of SNe II, although partial filling of the Hα absorption trough by emission associated with circumstellar interaction cannot be excluded. SN 2025abyc otherwise follows the general photospheric velocity evolution of SNe II, while remaining towards the high-velocity side of the comparison distribution in Hα, Hα, and Fe II. Exploratory light-curve modelling suggests a synthesised 56Ni mass of approximately 0.03–0.04 M⊙. We suggest that the extended circumstellar environment, 56Ni distribution, and hydrogen-envelope structure could all play a role in shaping the observed light-curve evolution, particularly the prolonged plateau-to-tail transition.
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BibTeX
@article{luhan2026prolonged,
title = {{A prolonged plateau-to-tail transition in the Type II supernova SN 2025abyc}},
author = {Li Luhan and Wang Bo and Zhang Jujia and Zhang Zhengyang and Luo Xinjie and Dong Shiyang and Xu Saien and Liu Zhengwei and Han Zhanwen},
journal = {Astronomy \& Astrophysics},
year = {2026},
month = oct,
doi = {10.1051/0004-6361/202661397},
url = {https://doi.org/10.1051/0004-6361/202661397},
note = {CC BY},
}
RIS
TY - JOUR
TI - A prolonged plateau-to-tail transition in the Type II supernova SN 2025abyc
AU - Li Luhan
AU - Wang Bo
AU - Zhang Jujia
AU - Zhang Zhengyang
AU - Luo Xinjie
AU - Dong Shiyang
AU - Xu Saien
AU - Liu Zhengwei
AU - Han Zhanwen
PY - 2026
DA - 2026/10/23
JO - Astronomy & Astrophysics
DO - 10.1051/0004-6361/202661397
UR - https://doi.org/10.1051/0004-6361/202661397
AB - We present optical photometric and spectroscopic observations of the Type II supernova (SN) SN 2025abyc. During the optically thick phase, which occurs approximately 10 and 70 d after explosion, its light curves show strongly wavelength-dependent decline rates of approximately 2.7, 2.1, 0.9, and 0.8 mag (100 d)−1 in the g, c, r, and o bands, respectively. At approximately 70 d, the light curves begin to depart from their nearly linear plateau evolution and gradually transition towards the radioactive tail. A Fermi–Dirac fit to the well-sampled ATLAS o-band light curve yields a transition midpoint of tPT ≈ 100.5 d. The interval between the end of the linear plateau and this transition midpoint is approximately 30 d, indicating a prolonged plateau-to-tail transition. This timescale is comparable to those measured for SN 2013by, SN 2013ej, and SN 2014G. Spectroscopically, at +13 d post-explosion, the Hα profile appears weak and broad, whereas Hβ and Hγ display clear P-Cygni profiles. This morphology can be explained by the normal early spectroscopic evolution of SNe II, although partial filling of the Hα absorption trough by emission associated with circumstellar interaction cannot be excluded. SN 2025abyc otherwise follows the general photospheric velocity evolution of SNe II, while remaining towards the high-velocity side of the comparison distribution in Hα, Hα, and Fe II. Exploratory light-curve modelling suggests a synthesised 56Ni mass of approximately 0.03–0.04 M⊙. We suggest that the extended circumstellar environment, 56Ni distribution, and hydrogen-envelope structure could all play a role in shaping the observed light-curve evolution, particularly the prolonged plateau-to-tail transition.
SN - 0004-6361
SN - 1432-0746
ER -