The Carnegie Supernova Project II

Observations of the intermediate-luminosity red transient SNhunt120^⋆,⋆⋆

¹ Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000 Aarhus C, Denmark
e-mail: max@phys.au.dk
² School of Physics, O’Brien Centre for Science North, University College Dublin, Belfield, Dublin 4, Ireland
³ Aarhus Institute of Advanced Studies (AIAS), Aarhus University, Høegh-Guldbergs Gade 6B, 8000 Aarhus C, Denmark
⁴ The George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, Texas A&M University, College Station, TX 877843, USA
⁵ Department of Physics and Astronomy, Texas A&M University, College Station, TX 77843, USA
⁶ Las Campanas Observatory, Carnegie Observatories, Casilla 601, La Serena, Chile
⁷ Nordic Optical Telescope, Apartado 474, 38700 Santa Cruz de La Palma, Spain
⁸ Departamento de Física Teórica y del Cosmos, Universidad de Granada, 18071 Granada, Spain
⁹ Núcleo de Astronomía de la Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Av. Ejército 441, Santiago, Chile
¹⁰ Millennium Institute of Astrophysics, Santiago, Chile
¹¹ Department of Physics, Florida State University, Tallahassee, FL 32306, USA
¹² Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 W. Brooks, Rm 100, Norman, OK 73019-2061, USA
¹³ Observatories of the Carnegie Institution for Science, 813 Santa Barbara St, Pasadena, CA 91101, USA
¹⁴ National Astronomical Observatory of Japan, National Institutes of Natural Sciences, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
¹⁵ School of Physics and Astronomy, Faculty of Science, Monash University, Clayton, VIC 3800, Australia
¹⁶ INAF – Osservatorio Astronomico di Capodimonte, Salita Moiarello 16, Napoli, Italy
¹⁷ Università degli studi di Catania, Dip. di Fisica e Astronomia “E. Majorana”, Via Santa Sofia 64, 95123 Catania, Italy
¹⁸ INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
¹⁹ Laboratori Nazionali del Sud-INFN, Via Santa Sofia 62, 95123 Catania, Italy
²⁰ SOAR Telescope, La Serena, 1700000, Chile

Received: 25 March 2020
Accepted: 15 May 2020

Abstract

We present multiwavelength observations of two gap transients that were followed by the Carnegie Supernova Project-II. The observations are 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 three days after outburst, the subsequent optical and near-infrared broadband followup extending over a period of about two months, 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 overestimate the luminosity. Finally, examination of pre-outburst Hubble Space Telescope images yields no progenitor detection.