The Carnegie Supernova Project II. Observations of the intermediate luminosity red transient SNhunt120

Abstract

We present multi-wavelength observations of two gap transients followed by the Carnegie Supernova Project-II and supplemented with data obtained by a number of different programs. Here in the first of two papers, we focus on the intermediate luminosity red transient (ILRT) designated SNhunt120, while in a companion paper we examine the luminous red novae AT 2014ej. Our data set for SNhunt120 consists of an early optical discovery, estimated to be within 3 days after outburst, the subsequent optical and nearinfrared broadband followup extending over a ∼2 month period, two visual-and two near-infrared wavelength spectra, and Spitzer Space Telescope observations extending from early (+28 d) to late (+1155 d) phases. SNhunt120 resembles other ILRTs such as NGC 300-2008-OT and SN 2008S, and like these other ILRTs, SNhunt120 exhibits prevalent mid-infrared emission at both early and late phases. From the comparison of SNhunt120 and other ILRTs to electron-capture supernova simulations, we find that the current models underestimate the explosion kinetic energy and thereby produce synthetic light curves that over-estimate the luminosity. Finally, examination of pre-outburst Hubble Space Telescope images yields no progenitor detection.

Intermediate Luminosity Red Transients by Black Holes Born from Erupting Massive Stars

“…In this work we find that the resulting emission is similar to what has been classified as intermediate luminosity red transients (ILRTs) observed in the previous decades (Kulkarni et al 2007;Botticella et al 2009;Smith et al 2009;Berger et al 2009;Bond et al 2009;Cai et al 2018;Jencson et al 2019;Williams et al 2020;Stritzinger et al 2020). The origin of ILRTs is not known, with several interpretations such as electroncapture supernovae or luminous blue variable-like mass eruptions.…”

The electron-capture origin of supernova 2018zd

“…Other ECSN candidates. In addition to SN 1054, other previously suggested ECSN candidates can be divided into three types: intermediate-luminosity red transients (ILRTs; e.g., SN 2008S and AT 2017be) 125,126,127,128,129,130 ; low-luminosity Type II-P SNe 7,8,17,38 ; and Type IIn-P SNe (e.g., SNe 2009kn and 2011ht) 131,132,18,29 (Extended Data Table 1).…”

“…ILRTs are the luminosity gap transients between novae and supernovae, whose origin has been debated as either a massive star outburst 133,134,135,136 or terminal ECSN explosion 125,126,127,128,129,130 .…”

Molecular remnant of Nova 1670 (CK Vulpeculae): I. Properties and enigmatic origin of the gas

“…Red novae are recognized as manifestations of on-going mergers of non-compact stars such as mainsequence dwarfs, sub-giants, or red giants (Soker, & Tylenda 2003;Tylenda, & Soker 2006;Tylenda et al 2011;Pastorello et al 2019). While the number of known red novae, mainly extragalactic ones, is quickly rising (e.g., Stritzinger et al 2020), we know only a few red-nova remnants that are decades old (Kamiński et al 2018a). The remnant of the 1670 eruption of CK Vul, as a candidate post-merger site, could be the oldest (counting from the onset of the eruption) known object of this type and as such offers the opportunity to investigate a merger aftermath centuries after the stellar coalescence.…”