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

Abstract

We present the results of the monitoring campaign of the Type IIn supernova (SN) 2018cnf (a.k.a. . It was discovered about ten days before the maximum light (on MJD=58 293.4 ± 5.7 in the V band, with M V = −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 and 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 M r = −14.66 ± 0.17 mag. This was likely an eruptive phase from the massive progenitor star that 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. 1 The source was also detected by the Asteroid Terrestrial-impact Last Alert System (ATLAS), labelled as ATLAS18vyq. Article number, page 1 of 19 Notes. GTC = 10.4 m Gran Telescopio Canarias (La Palma, Canary Islands, Spain); LT = 2.0 m Liverpool Telesope (La Palma, Canary Islands, Spain); FTN = 2.0 m Faulkes Telescope North (Haleakala, Hawaii Islands, USA); VLT = 8.2 m Very Large Telescope (ESO-Cerro Paranal, Chile); Copernico = 1.82 m Copernico Telescope (Mt. Ekar, Asiago Observatory, Italy); FTS = 2.0m Faulkes Telescope South (Siding Spring, Australia); NTT = 3.58 m New Technology Telescope (ESO-La Silla, Chile); Baade = 6.5 m Magellan Baade Telescope (Las Campanas Observatory, Chile).

Unveiling the Nature of SN 2011fh: a Young and Massive Star Gives Rise to a Luminous SN 2009ip-like Event

“…As described in Section 3.2 and shown in Figure 7, SN 2011fh, SN 2009ip (Mauerhan et al 2013), SN 2016bdu (Pastorello et al 2017, and Pastorello et al 2019), and SN 2011fh at ∼ 3.4 × 10 42 erg s −1 (Figure 9). The interpretation of the precursor event and its connection to the brighter one is still unclear, with ideas ranging from an explosion (faint core-collapse or a major outburst in a massive star) followed by ejecta-CSM interaction (Moriya 2015;Elias-Rosa et al 2016;Pastorello et al 2017), an outburst preceding a SN (Ofek et al 2013;Pastorello et al 2017), or the result of binary interactions (Kashi et al 2013;Levesque et al 2014;Goranskij et al 2016).…”

“…Pre-explosion images also showed progenitor variability similar to that of SN 2009ip. SN 2018cnf (Pastorello et al 2019) also had a sequence of two bright explosions, after years of explosive variability with eruptions reaching M r ∼ −14.7. Pastorello et al (2019) proposed a massive hypergiant or an LBV star as a plausible progenitor for SN 2018cnf.…”

“…SN 2018cnf (Pastorello et al 2019) also had a sequence of two bright explosions, after years of explosive variability with eruptions reaching M r ∼ −14.7. Pastorello et al (2019) proposed a massive hypergiant or an LBV star as a plausible progenitor for SN 2018cnf. More recently, the event AT2016jbu/Gaia16cfr showed a variable behavior followed by two bright explosions (Kilpatrick et al 2018;Brennan et al 2021a,b).…”

A systematic reclassification of Type IIn supernovae

“…SN 2009ip was initially recognised as an "SN impostor" (see Section 1.1.3) at its 2009 eruption, and then in 2012 it evolved into a SN IIn following its terminal explosion or a period of eruptive mass loss from its luminous blue variable (LBV) progenitor (see Section 1.1.1; Mauerhan et al 2013Ofek et al 2014, Pastorello et al 2017. This latter mode of mass loss was also observed in SN 2015bh (Boian & Groh 2018), SN 2016bdu (Pastorello et al 2017), and SN 2018cnf (Pastorello et al 2019b).…”

SN 2018gjx reveals that some SNe Ibn are SNe IIb exploding in dense circumstellar material

“…Morozova, Piro & Valenti 2017;Hosseinzadeh et al 2018a), delayed shock-breakout (SBO) due to dense very close-by CSM (Förster et al 2018), or from signatures in their early spectra such as the presence of He II and H recombination lines ('flash-ionization'; Benetti et al 1994;Gal-Yam et al 2014;Gangopadhyay et al 2020). Less directly, the presence of CSM material can be inferred from precursor mass-loss events (sometimes known as 'SN impostors'), which result in a burst of increased luminosity in the years prior to explosion and for which the terminal explosion of the star may also be seen (Pastorello et al 2007(Pastorello et al , 2013Mauerhan et al 2013;Margutti et al 2014;Ofek et al 2016;Pastorello et al 2019). The vast majority of SE-SNe, however, show no conspicuous signs of strong interaction in the optical in the first few hundred days, although there are an increasing number of exceptions (e.g.…”