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Unmasking the Progenitors and Energy Sources of Superluminous Supernovae

Periodic Reporting for period 1 - SUPERS (Unmasking the Progenitors and Energy Sources of Superluminous Supernovae)

Reporting period: 2018-09-01 to 2020-08-31

In the past decade, a population of supernovae with luminosities 10s-100x higher than those of ordinary core-collapse and Type Ia supernovae have been discovered. These so-called "superluminous" supernovae challenge our understanding of the physical mechanisms behind supernova explosions, and of the evolution and final fates of massive stars. This action aimed to shed light on this mysterious population of rare and extreme stellar explosions through several complimentary approaches: systematically collecting a large sample for the first time using data from the ongoing Zwicky Transient Facility project; through studying their late-time spectra looking for signatures of different powering mechanisms; and studying the explosion sites within their galaxies using resolved imaging from the Hubble Space Telescope.
The study of late-time spectra resulted in the discovery of a new signature of mass loss in superluminous supernovae, which resulted in both a Nature Astronomy publication and a new observational campaign at the Very Large Telescope to constrain the occurrence rate of this signature. This result has also been presented at several international conferences. Using the Zwicky Transient Facility to collect a large and well-determined sample of superluminous supernovae was also successful; the initial results are published and several sample papers (including one on rates, which was a main objective of this action) are in preparation. The final project on host galaxies is in progress.
See above. The discovery of superluminous supernovae having massive circumstellar shells was unexpected, but very exciting in the sense that it links this population to various mechanisms that are important to understand also for the formation of the massive black holes that are observed by gravitational wave experiments like LIGO/Virgo. The action has also contributed to collecting the largest uniform sample of superluminous supernovae to date, which will serve as a benchmark for future studies.
Light curves of four superluminous supernovae from ZTF, illustrating the diversity in the population