Article

The Type I superluminous supernova catalogue – II. Spectroscopic evolution in the photospheric phase, velocity measurements, and constraints on diversity

A. AamerAstrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast , Belfast BT7 1NN ,M. NichollAstrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast , Belfast BT7 1NN ,Sebastián GómezCenter for Astrophysics | Harvard & Smithsonian , 60 Garden Street, Cambridge, MA 02138-1516 ,E. BergerCenter for Astrophysics | Harvard & Smithsonian , 60 Garden Street, Cambridge, MA 02138-1516 ,P. K. BlanchardCenter for Astrophysics | Harvard & Smithsonian , 60 Garden Street, Cambridge, MA 02138-1516 ,J. P. AndersonEuropean Southern Observatory , Alonso de Córdova 3107, Casilla 19, Santiago ,C. R. AngusAstrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast , Belfast BT7 1NN ,Amar AryanGraduate Institute of Astronomy, National Central University , 300 Jhongda Road, 32001 Jhongli ,C. AshallInstitute for Astronomy, University of Hawai’i , 2680 Woodlawn Drive, Honolulu HI 96822 ,T. W. ChenGraduate Institute of Astronomy, National Central University , 300 Jhongda Road, 32001 Jhongli ,G. DimitriadisLancaster University Department of Physics, , Lancaster LA1 4YB ,L. GalbanyInstitut d’Estudis Espacials de Catalunya (IEEC) , E-08860 Castelldefels (Barcelona) ,A. GkiniStockholm University, Albanova University Center The Oskar Klein Centre, Department of Astronomy, , SE-106 91 Stockholm ,M. GromadzkiAstronomical Observatory, University of Warsaw , Al. Ujazdowskie 4, PL-00-478 Warszawa ,C. P. GutiérrezInstitut d’Estudis Espacials de Catalunya (IEEC) , E-08860 Castelldefels (Barcelona) ,Daichi HiramatsuCenter for Astrophysics | Harvard & Smithsonian , 60 Garden Street, Cambridge, MA 02138-1516 ,Griffin HosseinzadehUniversity of California Department of Astronomy & Astrophysics, , San Diego, 9500 Gilman Drive, MC 0424, La Jolla, CA 92093-0424 ,C. InserraCardiff Hub for Astrophysics Research and Technology, School of Physics & Astronomy, Cardiff University , Queens Buildings, The Parade, Cardiff CF24 3AA ,Amit KumarUniversity of London Department of Physics, Royal Holloway, , Egham TW20 0EX ,Harsh KumarCenter for Astrophysics | Harvard & Smithsonian , 60 Garden Street, Cambridge, MA 02138-1516 ,H. KuncarayaktiUniversity of Turku Finnish Centre for Astronomy with ESO (FINCA), , FI-20014 Turku ,G. LeloudasDTU Space, National Space Institute, Technical University of Denmark , Elektrovej 327, DK-2800 Kgs. Lyngby ,P. A. MazzaliAstrophysics Research Institute, Liverpool John Moores University , 146 Brownlow Hill, Liverpool L3 5RF ,K. MedlerInstitute for Astronomy, University of Hawai’i , 2680 Woodlawn Drive, Honolulu HI 96822 ,T. E. Müller-BravoInstituto de Ciencias Exactas y Naturales (ICEN), Universidad Arturo Prat , Santiago 8370133 ,Mauricio RamírezMillennium Institute of Astrophysics MAS, Nuncio Monsenor Sotero Sanz 100 , Off. 104, Providencia, Santiago 7500011 ,A. K.Graduate Institute of Astronomy, National Central University , 300 Jhongda Road, 32001 Jhongli ,S. SchulzeNorthwestern University Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) and Department of Physics and Astronomy, , Evanston, IL 60208 ,Avinash SinghStockholm University, Albanova University Center The Oskar Klein Centre, Department of Astronomy, , SE-106 91 Stockholm ,J. SollermanStockholm University, Albanova University Center The Oskar Klein Centre, Department of Astronomy, , SE-106 91 Stockholm ,Shubham SrivastavUniversity of Oxford Astrophysics sub-Department, Department of Physics, , Keble Road, Oxford OX1 3RH ,J. TerwelSchool of Physics, Trinity College Dublin, The University of Dublin , Dublin 2, D02 PN40 ,D. R. YoungAstrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast , Belfast BT7 1NN ,

2025en

ABI

Abstract

ABSTRACT Hydrogen-poor superluminous supernovae (SLSNe) are among the most energetic explosions in the universe, reaching luminosities up to 100 times greater than those of normal supernovae. This paper presents the largest compilation of SLSN photospheric spectra to date, encompassing data from the advanced Public ESO Spectroscopic Survey of Transient Objects (ePESSTO+), the Finding Luminous and Exotic Extragalactic Transients (FLEET) search, and all published spectra up to December 2022. The data set includes a total of 974 spectra of 234 SLSNe. By constructing average phase binned spectra, we find SLSNe initially exhibit high temperatures (10 000–11 000 K), with blue continua and weak lines. A rapid transformation follows, as temperatures drop to 5000–6000 K by 40 d post-peak, leading to stronger P-Cygni features. Variance within the data set is slightly reduced when defining the phase of spectra relative to explosion, rather than peak, and normalising to the population’s median e-folding decline time. Principal Component Analysis (PCA) supports this, requiring fewer components to explain the same level of variation when binning data by scaled days from explosion, suggesting a more homogeneous grouping. Using PCA and K-means clustering, we identify outlying objects with unusual spectroscopic evolution and evidence for energy input from interaction, but find no support for groupings of two or more statistically significant subpopulations. We find Fe ii $\lambda$5169 line velocities closely track the radius implied from blackbody fits, indicating formation near the photosphere. We also confirm a correlation between velocity and velocity gradient, which can be explained if all SLSNe are in homologous expansion but with different scale velocities. This behaviour aligns with expectations for an internal powering mechanism.

Identifiers

DOI: 10.1093/mnras/staf1113

Citations and references

Cited by 10 references

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