Is supernova SN 2020faa an iPTF14hls look-alike?^⋆

¹ Department of Astronomy, The Oskar Klein Center, Stockholm University, , AlbaNova 10691, Stockholm, Sweden
e-mail: sheng.yang@astro.su.se
² Department of Particle Physics and Astrophysics, Weizmann Institute of Science, 234 Herzl St, 76100 Rehovot, Israel
³ Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
⁴ Caltech Optical Observatories, California Institute of Technology, Pasadena, CA 91125, USA
⁵ Texas Tech University, Department of Physics & Astronomy, Box 41051, 79409 Lubbock, TX, USA
⁶ Division of Physics, Mathematics and Astronomy, California Institute of Technology, Pasadena, CA 91125, USA
⁷ Center for Data Driven Discovery, California Institute of Technology, Pasadena, CA 91125, USA
⁸ IPAC, California Institute of Technology, 1200 E. California, Blvd, Pasadena, CA 91125, USA
⁹ Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA
¹⁰ Department of Astronomy, University of California, Berkeley, CA 94720-3411, USA
¹¹ Astrophysics Research Institute, Liverpool John Moores University, IC2, Liverpool Science Park, 146 Brownlow Hill, Liverpool L3 5RF, UK

Received: 15 September 2020
Accepted: 2 November 2020

Abstract

Context. We present observations of ZTF20aatqesi (SN 2020faa). This Type II supernova (SN) displays a luminous light curve (LC) that started to rebrighten from an initial decline. We investigate this in relation to the famous SN iPTF14hls, which received a great deal of attention and multiple interpretations in the literature, but whose nature and source of energy still remain unknown.

Aims. We demonstrate the great similarity between SN 2020faa and iPTF14hls during the first 6 months, and use this comparison to forecast the evolution of SN 2020faa and to reflect on the less well observed early evolution of iPTF14hls.

Methods. We present and analyse our observational data, consisting mainly of optical LCs from the Zwicky Transient Facility in the gri bands and of a sequence of optical spectra. We construct colour curves and a bolometric lc, and we compare ejecta-velocity and black-body radius evolutions for the two supernovae (SNe) and for more typical Type II SNe.

Results. The LCs show a great similarity with those of iPTF14hls over the first 6 months in luminosity, timescale, and colour. In addition, the spectral evolution of SN 2020faa is that of a Type II SN, although it probes earlier epochs than those available for iPTF14hls.

Conclusions. The similar LC behaviour is suggestive of SN 2020faa being a new iPTF14hls. We present these observations now to advocate follow-up observations, since most of the more striking evolution of SN iPTF14hls came later, with LC undulations and a spectacular longevity. On the other hand, for SN 2020faa we have better constraints on the explosion epoch than we had for iPTF14hls, and we have been able to spectroscopically monitor it from earlier phases than was done for the more famous sibling.