Published January 2026 | Version Published
Journal Article Open

SN 2023gpw: Exploring the diversity and power sources of hydrogen-rich superluminous supernovae

  • 1. ROR icon University of Turku
  • 2. ROR icon Aalto University
  • 3. ROR icon California Institute of Technology
  • 4. ROR icon Aarhus University
  • 5. ROR icon Northwestern University
  • 6. ROR icon Osservatorio Astronomico di Padova
  • 7. ROR icon Institute of Space Sciences
  • 8. ROR icon Liverpool John Moores University
  • 9. ROR icon Stockholm University
  • 10. ROR icon Trinity College Dublin
  • 11. ROR icon Arturo Prat University
  • 12. ROR icon Institut d'Estudis Espacials de Catalunya
  • 13. ROR icon Infrared Processing and Analysis Center

Abstract

We present our observations and analysis of SN 2023gpw, a hydrogen-rich superluminous supernova (SLSN II) with broad emission lines in its post-peak spectra. Unlike previously observed SLSNe II, its light curve suggests an abrupt drop during a solar conjunction between ∼80 and ∼180 d after the light curve peak, which is possibly analogous to a normal hydrogen-rich supernova (SN). Spectra taken at and before the peak show hydrogen and helium “flash” emission lines attributed to early interaction with a dense confined circumstellar medium (CSM). A well-observed ultraviolet excess appears as these lines disappear, also as a result of CSM interaction. The blackbody photosphere expands roughly at the same velocity throughout the observations, indicating little or no bulk deceleration. This velocity is much higher than what is seen in spectral lines, suggesting asymmetry in the ejecta. The high total radiated energy (≳9 × 1050 erg) and aforementioned lack of bulk deceleration in SN 2023gpw are difficult to reconcile with a neutrino-driven SN simply combined with efficient conversion from kinetic energy to emission through interaction. This suggests an additional energy source, such as a central engine. While magnetar-powered models qualitatively similar to SN 2023gpw exist, more modeling work is required to determine if they can reproduce the observed properties in combination with early interaction. The required energy might alternatively be provided by accretion onto a black hole created in the collapse of a massive progenitor star.

Copyright and License

© The Authors 2026. Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Acknowledgement

We thank the anonymous referee for useful comments, and Georgios Dimitriadis for re-reducing the INT spectrum. T.K. acknowledges support from the Research Council of Finland project 360274. R.K. and T.L.K. acknowledge support from the Research Council of Finland (340613). M.S. is funded by the Independent Research Fund Denmark (IRFD) via Project 2 grant 10.46540/2032-00022B and by the Aarhus University Nova grant# AUFF-E-2023-9-28. N.E.R. acknowledges support from the PRIN-INAF 2022, ‘Shedding light on the nature of gap transients: from the observations to the models’ and 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. C.P.G. acknowledges financial support from the Secretary of Universities and Research (Government of Catalonia) and by the Horizon 2020 Research and Innovation Programme of the European Union under the Marie Skłodowska-Curie and the Beatriu de Pinós 2021 BP 00168 programme, from the Spanish Ministerio de Ciencia e Innovación (MCIN) and the Agencia Estatal de Investigación (AEI) 10.13039/501100011033 under the PID2023-151307NB-I00 SNNEXT project, from Centro Superior de Investigaciones Científicas (CSIC) under the PIE project 20215AT016 and the program Unidad de Excelencia María de Maeztu CEX2020-001058-M, and from the Departament de Recerca i Universitats de la Generalitat de Catalunya through the 2021-SGR-01270 grant. T.L.K. acknowledges a Warwick Astrophysics prize post-doctoral fellowship made possible thanks to a generous philanthropic donation. T.E.M.B. is funded by Horizon Europe ERC grant no. 101125877. The Starlink software (Currie et al. 2014) is currently supported by the East Asian Observatory. This study is based on observations made with the Gran Telescopio Canarias (GTC), installed in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias, in the island of La Palma. Access to the Las Cumbres Observatory was made possible via an allocation by OPTICON (program 22A/012, PI Stritzinger). This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 101004719. Based on observations obtained with the Samuel Oschin Telescope 48-inch and the 60-inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under Grant No. AST-2034437 and a collaboration including Caltech, IPAC, the Weizmann Institute of Science, the Oskar Klein Center at Stockholm University, the University of Maryland, Deutsches Elektronen-Synchrotron and Humboldt University, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, Trinity College Dublin, Lawrence Livermore National Laboratories, IN2P3, University of Warwick, Ruhr University Bochum, Cornell University, and Northwestern University. Operations are conducted by COO, IPAC, and UW.

Data Availability

All spectra presented in this paper are available for download on WISEREP (Yaron & Gal-Yam 2012) at https://www.wiserep.org/object/23362.

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Additional details

Related works

Is new version of
Discussion Paper: arXiv:2505.17518 (arXiv)
Is supplemented by
Dataset: https://www.wiserep.org/object/23362 (URL)

Funding

Research Council of Finland
360274
Research Council of Finland
340613
Danmarks Frie Forskningsfond
10.46540/2032-00022B
Aarhus University
AUFF-E-2023-9-28
National Institute for Astrophysics
PRIN-INAF 2022
Ministerio de Ciencia, Innovación y Universidades
PID2023-151307NB-I00
Centro Superior de Investigaciones Cientificas
CEX2020-001058-M
Secretary of Universities and Research
European Research Council
BP 00168
Agencia Estatal de Investigación
10.13039/501100011033
Centro Superior de Investigaciones Cientificas
20215AT016
Departament de Recerca i Universitats de la Generalitat de Catalunya
2021-SGR-01270
European Research Council
101125877
European Research Council
101004719
National Science Foundation
AST-2034437

Dates

Submitted
2025-05-20
Accepted
2025-09-14
Available
2026-01-06
Published online