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An international team of astronomers has inspected an unusual superluminous supernova known as SN 2020wnt. Results of the study suggest that this supernova is slowly evolving and carbon-rich. The finding was detailed in a paper published June 3 on the arXiv pre-print server.

Supernovae (SNe) are powerful and luminous stellar explosions. They are important for the scientific community as they offer essential clues into the evolution of stars and galaxies. In general, SNe are divided into two groups based on their atomic spectra: Type I and Type II. Type I SNe lack hydrogen in their spectra, while those of Type II showcase spectral lines of hydrogen.

Superluminous supernovae (SLSNe) are characterized by exceptionally bright, often long-lived light curves. Interaction of the SN ejecta with surrounding circumstellar material (CSM) is an efficient mechanism to convert kinetic energy of the ejecta into radiation, and it is assumed that such a process may power SLSNe.

SN 2020wnt (also known as ZTF20acjeflr and ATLAS20beko) was detected by the Zwicky Transient Facility (ZTF) on October 14, 2020, at a magnitude of 19.7. Subsequent observations of SN 2020wnt suggested that it is a Type I supernova at a redshift of 0.032. The host of this SN is a faint galaxy known as WISEA J034638.04+431348.3.

Now, a group of astronomers led by Claudia Gutiérrez of the University of Turku in Finland, present the results of new observations of SN 2020wnt that shed more light on the properties of this supernova. Most of these observations were carried out by two wide-field imaging surveys—Asteroid Terrestrial Impact Last Alert System (ATLAS) and Zwicky Transient Facility (ZTF).

The new research found that the light curves of SN 2020wnt showcase an early bump lasting about five days followed by a slow rise to the main peak. It was added that the peak is reached at different times, occurring faster in the bluer bands, while the peak absolute magnitude of around −20.5 mag was recorded some 77 days after the explosion.

Furthermore, about 130 days after the explosion, the light curves show a linear decline in all bands. Later, from the 273rd day since the explosion, a sudden drop in brightness is observed, which suggests a significant leakage of gamma-ray photons. The last observation made by Gutiérrez's team, which started 350 days after the explosion, shows an increase in brightness, indicating an interaction between the ejecta and the circumstellar medium (CSM).

The researchers also found that the optical spectra of SN 2020wnt display clear lines of ionized carbon (C II) and silicon (Si II), while the classical oxygen (O II) lines that typically characterize Type I SLSNe are not detected. This probably related to the low temperatures of this SN (below 10,000 K).

Therefore, the authors of the paper concluded that SN 2020wnt is a slowly evolving carbon-rich SLSN. They assume that the progenitor of this SN had mass of around 80 solar masses, a radius of about 15 solar radii, and the explosion energy was at a level of approximately 45 sexdecillion ergs.

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