The Carnegie Supernova Project II Observations of the intermediate-luminosity red transient SNhunt120 Stritzinger, M. D. Galbany González, Lluis Supernovae: individual: SNhunt120 Supernovae: general 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 midinfrared 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. 2020-10-05T12:52:49Z 2020-10-05T12:52:49Z 2020-07 journal article Stritzinger, M. D., Taddia, F., Fraser, M., Tauris, T. M., Suntzeff, N. B., Contreras, C., ... & Phillips, M. M. (2020). The Carnegie Supernova Project II. Observations of the intermediate luminosity red transient SNhunt120. arXiv preprint arXiv:2005.00319. [https://doi.org/10.1051/0004-6361/202038018] http://hdl.handle.net/10481/63670 10.1051/0004-6361/202038018 eng http://creativecommons.org/licenses/by/3.0/es/ open access Atribución 3.0 España EDP Sciences