SN 2017ckj: A linearly declining type IIb supernova with a relatively massive hydrogen envelope

We present optical observations of the type IIb supernova (SN) 2017ckj, covering approximately 180 days after the explosion. Its early-time multi-band light curves display no clear evidence of a shock-cooling tail, resembling the behaviour of SN 2008ax. The V -band light curve exhibits a short rise time of about 5 days and reaches an absolute fitted peak magnitude of M V = −18.49 ± 0.18 mag. The late-time multi-band light curves reveal a linear decline. We modelled the bolometric light curve of SN 2017ckj to constrain the progenitor and the explosion parameters. We estimated a total mass of 56 Ni synthesised by SN 2017ckj of M Ni = 0.21 +0.05 −0.03 M ⊙ , with a massive H-rich envelope of M env = 0.4 +0.1 −0.1 M ⊙ . Both the 56 Ni mass and the envelope mass of SN 2017ckj are higher than those of typical SNe IIb, in agreement with its peculiar light curve evolution. The early-time spectra of SN 2017ckj are dominated by a blue continuum, accompanied by narrow H α and He II emission lines. The earliest spectrum exhibits flash ionisation features, from which we estimated a progenitor mass-loss rate of ∼3 × 10 −4 M ⊙ yr −1 . At later epochs, the spectra develop broad P-Cygni profiles and become increasingly similar to those of SNe IIb, especially SN 2018gk. The late-time spectrum at around 139 days does not show a distinct decline in the strength of its H α emission profile, also indicating a relatively massive envelope of its progenitor. Aside from the H α feature, the nebular spectrum exhibits prominent emission lines of O I , Ca II , [Ca II ], and Mg I ], which are consistent with the prototypical SN 1993J.

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Journal
Astronomy and Astrophysics
Published
2025-11-04
DOI
https://doi.org/10.1051/0004-6361/202556873
Primary Topic
Gamma-ray bursts and supernovae
Type
article
Field-Weighted Citation Impact
0.00

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article

SN 2017ckj: A linearly declining type IIb supernova with a relatively massive hydrogen envelope

L. Tomasella, A. Pastorello, I. Salmaso, P. Ochner et al.
Astronomy and Astrophysics
Gamma-ray bursts and supernovae
article

SN 2017ckj: A linearly declining type IIb supernova with a relatively massive hydrogen envelope

L. Tomasella, A. Pastorello, I. Salmaso, P. Ochner, M. Fraser, M. Gromadzki, G. Valerin, S. Benetti, A. Reguitti, Zhongmin Peng, Yongzhi Cai, A. Fiore, J.-J. Zhang, S. Mattila, M. Stritzinger, Peter Lundqvist, E. Kankare, Tim Reynolds, Bo Wang, T. Kangas, E. Cappellaro, N. Elias–Rosa, J. Isern, J. Harmanen, Shubham Srivastav, Hua-Li Li, Chao Wu, Zhenru Wang, L. Borsato
article en

Abstract

We present optical observations of the type IIb supernova (SN) 2017ckj, covering approximately 180 days after the explosion. Its early-time multi-band light curves display no clear evidence of a shock-cooling tail, resembling the behaviour of SN 2008ax. The V -band light curve exhibits a short rise time of about 5 days and reaches an absolute fitted peak magnitude of M V = −18.49 ± 0.18 mag. The late-time multi-band light curves reveal a linear decline. We modelled the bolometric light curve of SN 2017ckj to constrain the progenitor and the explosion parameters. We estimated a total mass of 56 Ni synthesised by SN 2017ckj of M Ni = 0.21 +0.05 −0.03 M ⊙ , with a massive H-rich envelope of M env = 0.4 +0.1 −0.1 M ⊙ . Both the 56 Ni mass and the envelope mass of SN 2017ckj are higher than those of typical SNe IIb, in agreement with its peculiar light curve evolution. The early-time spectra of SN 2017ckj are dominated by a blue continuum, accompanied by narrow H α and He II emission lines. The earliest spectrum exhibits flash ionisation features, from which we estimated a progenitor mass-loss rate of ∼3 × 10 −4 M ⊙ yr −1 . At later epochs, the spectra develop broad P-Cygni profiles and become increasingly similar to those of SNe IIb, especially SN 2018gk. The late-time spectrum at around 139 days does not show a distinct decline in the strength of its H α emission profile, also indicating a relatively massive envelope of its progenitor. Aside from the H α feature, the nebular spectrum exhibits prominent emission lines of O I , Ca II , [Ca II ], and Mg I ], which are consistent with the prototypical SN 1993J.

Astronomy and AstrophysicsVol. 704
University College Dublin (IE), Chongqing University of Posts and Telecommunications (CN), University of Copenhagen (DK), Queen's University Belfast (GB), University of Turku (FI), Stockholm University (SE), Turku Centre for Computer Science (FI), Yunnan University (CN), European University Cyprus (CY), Aarhus University (DK), Beijing Normal University (CN), Istituto Nazionale di Fisica Nucleare, Galileo Galilei Institute for Theoretical Physics (IT), Yunnan Observatories (CN), Astronomical Observatory of Capodimonte (IT), Brera Astronomical Observatory (IT), Institut d'Estudis Espacials de Catalunya (ES), Institute of Space Sciences (ES), DAWN Center for Independent Living (US), Reial Acadèmia de Ciències i Arts de Barcelona (ES), Collurania Teramo Observatory (IT), Astronomical Observatory (RS), Osservatorio Astronomico di Padova (IT), University of Chinese Academy of Sciences (CN), University of Warsaw (PL)
Aarhus Universitet, European Commission, National Research Foundation, Danmarks Grundforskningsfond, National Natural Science Foundation of China, Suomalainen Tiedeakatemia, Universitetet i Oslo, Háskóli Íslands, Turun Yliopisto, Stockholms Universitet, National Key Research and Development Program of China
Openalex Percentile: Top 77%
Gamma-ray bursts and supernovae
DOIOpen Access PDFOpenAlex
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