SN 2017ati: A luminous type IIb explosion from a massive progenitor;
: Peng, Z.-H.; Benetti, S.; Cai, Y.-Z.; Pastorello, A.; Zhao, J.-W.; Reguitti, A.; Wang, Z.-Y.; Cappellaro, E.; Elias-Rosa, N.; Fang, Q.-L.; Fraser, M.; Kangas, T.; Kankare, E.; Kostrzewa-Rutkowska, Z.; Lundqvist, P.; Mattila, S.; Reynolds, T. M.; Stritzinger, M. D.; Somero, A.; Tomasella, L.; Pei, S.-P.; Yang, Y.-J.; Zhang, J.-J.; Pan, Y.
Publisher: EDP Sciences
: 2026
Astronomy and Astrophysics
: A156
: 709
: 0004-6361
: 1432-0746
DOI: https://doi.org/10.1051/0004-6361/202659331
: https://doi.org/10.1051/0004-6361/202659331
: https://research.utu.fi/converis/portal/detail/Publication/524889509
We present optical photometric and spectroscopic observations of the Type IIb supernova (SN) 2017ati. It reached maximum light about 27 d after explosion, and the light curve shows a broad, luminous peak with an absolute r-band magnitude of Mr = −18.48 ± 0.16 mag. At about 50 d after maximum light, SN 2017ati exhibited a decline rate close to that expected from the 56Co →56Fe radioactive decay, at 0.98 mag per 100 days, as is usually observed in SNe IIb. However, it remains systematically brighter at late times by about 1–2 mag, exceeding the usual upper luminosity range of this class. As a result, modelling the light curve of SN 2017ati with a standard 56Ni decay scenario requires a large nickel mass of up to ∼0.37 M⊙ and still fails to reproduce the early-time light curve adequately. In contrast, incorporating additional energy input from a magnetar yields a significantly improved fit to the light curve of SN 2017ati, which would reduce the nickel mass to ∼0.21 M⊙, which is still close to the upper end of the range typically inferred for SNe IIb. Comparing the fitted results of SN 2017ati with the known sample of SNe IIb indicates that its luminosity evolution is best explained by a combination of neutron star spin-down energy and radioactive nickel deposition. From late-time nebular spectra of SN 2017ati, the luminosity of the [O I] λλ6300, 6364 doublet implies an oxygen mass of ∼1.82 − 3.34 M⊙, and the combination of a [Ca II]/[O I] flux ratio of ∼0.5 with nebular spectral model comparisons favours a progenitor zero-age main-sequence mass of ≥17 M⊙.
supernovae: individual: SN 2017ati
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This work is supported by the National Natural Science Foundation of China (No. 12303054), the National Key Research and Development Program of China (Grant No. 2024YFA1611603), the Yunnan Fundamental Research Projects (Grant Nos. 202401AU070063, 202501AS070078), and the International Centre of Supernovae, Yunnan Key Laboratory (No. 202302AN360001). Y.-Z.C. and A.R. acknowledge financial support from the SOXS project (PI S. Campana). AP, AR, SB, EC, NER and LT acknowledge support from the PRIN-INAF 2022, “Shedding light on the nature of gap transients: from the observations to the models”. EC acknowledges support from MIUR, PRIN 2020 (METE, grant 2020KB33TP). N.E.R. also acknowledges support from the Spanish Ministerio de Ciencia e Innovación (MCIN) and the Agencia Estatal de Investigación (AEI) 10.13039/501100011033 under the program Unidad de Excelencia María de Maeztu CEX2020-001058-M. T.K. acknowledges support from the Research Council of Finland project 360274. T.M.R. is part of the Cosmic Dawn Center (DAWN), which is funded by the Danish National Research Foundation under grant DNRF140. T.M.R and S. Mattila acknowledge support from the Research Council of Finland project 350458. M.D.S. is funded by the Independent Research Fund Denmark (IRFD, grant number 10.46540/2032-00022B). S.-P. Pei is supported by the Science and Technology Foundation of Guizhou Province (QKHJCMS[2026]752). Y.-J. Yang is supported by the National Natural Science Foundation of China (Grants No. 12305066). We thank Luhan Li for providing some public datasets of comparison objects. Based on observations obtained with the Cima Ekar 1.82 m Telescopio Copernico, installed at the INAF (Istituto Nazionale di Astrofisica) – Astronomical Observatory of Padova, Italy. Based on observations made with the Nordic Optical Telescope (NOT), owned in collaboration by the University of Turku and Aarhus University, and operated jointly by Aarhus University, the University of Turku, and the University of Oslo, representing Denmark, Finland, and Norway, the University of Iceland, and Stockholm University at the Observatorio del Roque de los Muchachos, La Palma, Spain, of the Instituto de Astrofisica de Canarias. We acknowledge ESA Gaia, DPAC and the Photometric Science Alerts Team (http://gsaweb.ast.cam.ac.uk/alerts). This work has made use of data from the Asteroid Terrestrial-impact Last Alert System (ATLAS) project. ATLAS is primarily funded to search for near-Earth objects through NASA grants NN12AR55G, 80NSSC18K0284, and 80NSSC18K1575; byproducts of the NEO search include images and catalogs from the survey area. The ATLAS science products have been made possible through the contributions of the University of Hawaii Institute for Astronomy, the Queen’s University Belfast, STScI, and the South African Astronomical Observatory, and The Millennium Institute of Astrophysics (MAS), Chile. We thank Las Cumbres Observatory and its staff for their continued support of ASAS-SN. ASAS-SN is funded in part by the Gordon and Betty Moore Foundation through grants GBMF5490 and GBMF10501 to the Ohio State University, and also funded in part by the Alfred P. Sloan Foundation grant G-2021-14192. Development of ASAS-SN has been supported by NSF grant AST-0908816, the Mt. Cuba Astronomical Foundation, the Center for Cosmology and AstroParticle Physics at the Ohio State University, the Chinese Academy of Sciences South America Center for Astronomy (CAS-SACA), and the Villum Foundation. This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. IRAF was distributed by the National Optical Astronomy Observatory, which was managed by the Association of Universities for Research in Astronomy (AURA), Inc., under a cooperative agreement with the U.S. NSF.
