The luminous and rapidly evolving SN 2018bcc. Clues toward the origin of Type Ibn SNe from the Zwicky Transient Facility

Creators: Karamehmetoglu, E.; Fransson, C.; Sollerman, J.; Tartaglia, L.; Taddia, F.; De, K.; Fremling, C.; Bagdasaryan, A.; Barbarino, C.; Bellm, E. C.; Dekany, R.; Dugas, A. M.; Giomi, M.; Goobar, A.; Graham, M.; Ho, A.; Laher, R. R.; Masci, F. J.; Neill, J. D.; Perley, D.; Riddle, R.; Rusholme, B.; Soumagnac, M. T.

Abstract

Context. Supernovae (SNe) Type Ibn are rapidly evolving and bright (M_(R, peak) ∼ −19) transients interacting with He-rich circumstellar material (CSM). SN 2018bcc, detected by the ZTF shortly after explosion, provides the best constraints on the shape of the rising light curve (LC) of a fast Type Ibn. Aims. We used the high-quality data set of SN 2018bcc to study observational signatures of the class. Additionally, the powering mechanism of SN 2018bcc offers insights into the debated progenitor connection of Type Ibn SNe. Methods. We compared well-constrained LC properties obtained from empirical models with the literature. We fit the pseudo-bolometric LC with semi-analytical models powered by radioactive decay and CSM interaction. Finally, we modeled the line profiles and emissivity of the prominent He I lines, in order to study the formation of P-Cygni profiles and to estimate CSM properties. Results. SN 2018bcc had a rise time to peak of the LC of 5.6_(−0.1)^(+0.2) days in the restframe with a rising shape power-law index close to 2, and seems to be a typical rapidly evolving Type Ibn SN. The spectrum lacked signatures of SN-like ejecta and was dominated by over 15 He emission features at 20 days past peak, alongside Ca and Mg, all with V_(FWHM) ∼ 2000 km s⁻¹. The luminous and rapidly evolving LC could be powered by CSM interaction but not by the decay of radioactive ⁵⁶Ni. Modeling of the He I lines indicated a dense and optically thick CSM that can explain the P-Cygni profiles. Conclusions. Like other rapidly evolving Type Ibn SNe, SN 2018bcc is a luminous transient with a rapid rise to peak powered by shock interaction inside a dense and He-rich CSM. Its spectra do not support the existence of two Type Ibn spectral classes. We also note the remarkable observational match to pulsational pair instability SN models.

Additional Information

© ESO 2021. Article published by EDP Sciences. Received 13 July 2019; Accepted 5 November 2019; Published online 01 June 2021. We gratefully acknowledge support from the Knut and Alice Wallenberg Foundation and the Swedish Research Council. 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. Major funding has been provided by the US National Science Foundation under Grant No. AST-1440341 and by the ZTF partner institutions: the California Institute of Technology, the Oskar Klein Centre, the Weizmann Institute of Science, the University of Maryland, the University of Washington, Deutsches Elektronen-Synchrotron, the University of Wisconsin-Milwaukee, and the TANGO Program of the University System of Taiwan. The Oskar Klein Centre is funded by the Swedish Research Council. This research is partially based on observations made with the Nordic Optical Telescope, operated by NOTSA at IAC using ALFOSC, which is provided by the IAA. Some of the data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA; the observatory was made possible by the generous financial support of the W.M. Keck Foundation. Some of the data presented herein were obtained with the Liverpool Telescope operated on the island of La Palma by Liverpool John Moores University in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias with financial support from the UK Science and Technology Facilities Council. This work is partly based on observations made with DOLoRes@TNG. This research made use of Astropy, a community-developed core Python package for Astronomy (Astropy Collaboration 2018) IRAF, is distributed by the National Optical Astronomy Observatories, which are operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation. The python version which was used, PyRAF, is a product of the Space Telescope Science Institute, which is operated by AURA for NASA. SED Machine is based upon work supported by the National Science Foundation under Grant No. 1106171. We would like to thank E. Ofek for his comments on the manuscript.

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