# A luminous stellar outburst during a long-lasting eruptive phase first, and then SN IIn 2018cnf

## TL;DR

SN 2018cnf exhibited a luminous outburst during a prolonged eruptive phase before exploding as a Type IIn supernova, with evidence of interaction with circumstellar material and a likely massive hypergiant progenitor.

## Contribution

This study provides detailed photometric and spectroscopic observations of SN 2018cnf, revealing its eruptive history and circumstellar environment, and compares it to similar transients like SN 2009ip.

## Key findings

- Pre-explosion variability indicating eruptive phase from 2011
- Spectral features showing ejecta-CSM interaction
- Progenitor likely a luminous blue variable hypergiant

## Abstract

We present the results of the monitoring campaign of the Type IIn supernova (SN) 2018cnf (aka ASASSN-18mr). It was discovered about 10 days before the maximum light (on MJD = 58293.4+-5.7 in the V band, with MV = -18.13+-0.15 mag). The multiband light curves show an immediate post-peak decline with some minor luminosity fluctuations, followed by a flattening starting about 40 days after maximum. The early spectra are relatively blue and show narrow Balmer lines with P Cygni profiles. Additionally, Fe II, O I, He I and Ca II are detected. The spectra show little evolution with time, with intermediate-width features becoming progressively more prominent, indicating stronger interaction of the SN ejecta with the circumstellar medium. The inspection of archival images from the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) survey has revealed a variable source at the SN position, with a brightest detection in December 2015 at Mr = -14.66+-0.17 mag. This was likely an eruptive phase from the massive progenitor star started from at least mid-2011, and that produced the circumstellar environment within which the star exploded as a Type IIn SN. The overall properties of SN 2018cnf closely resemble those of transients such as SN 2009ip. This similarity favours a massive hypergiant, perhaps a luminous blue variable, as progenitor for SN 2018cnf.