ELIAS DE LA ROSA, NANCY DEL CARMENNANCY DEL CARMENELIAS DE LA ROSABENETTI, StefanoStefanoBENETTICAPPELLARO, EnricoEnricoCAPPELLAROPASTORELLO, AndreaAndreaPASTORELLOTerreran, G.G.TerreranMorales-Garoffolo, A.A.Morales-GaroffoloHowerton, S. C.S. C.HowertonValenti, S.S.ValentiKankare, E.E.KankareDrake, A. J.A. J.DrakeDjorgovski, S. G.S. G.DjorgovskiTOMASELLA, LinaLinaTOMASELLATARTAGLIA, LeonardoLeonardoTARTAGLIAKangas, T.T.KangasOchner, P.P.OchnerFilippenko, A. V.A. V.FilippenkoCiabattari, F.F.CiabattariGeier, S.S.GeierHowell, D. A.D. A.HowellIsern, J.J.IsernLeonini, S.S.LeoniniPignata, G.G.PignataTURATTO, MassimoMassimoTURATTO2020-10-222020-10-2220180035-8711http://hdl.handle.net/20.500.12386/27934SNhunt151 was initially classified as a supernova (SN) impostor (nonterminal outburst of a massive star). It exhibited a slow increase in luminosity, lasting about 450 d, followed by a major brightening that reaches M_V ≈ -18 mag. No source is detected to M_V ≳ -13 mag in archival images at the position of SNhunt151 before the slow rise. Low-to-mid-resolution optical spectra obtained during the pronounced brightening show very little evolution, being dominated at all times by multicomponent Balmer emission lines, a signature of interaction between the material ejected in the new outburst and the pre-existing circumstellar medium. We also analysed mid-infrared images from the Spitzer Space Telescope, detecting a source at the transient position in 2014 and 2015. Overall, SNhunt151 is spectroscopically a Type IIn SN, somewhat similar to SN 2009ip. However, there are also some differences, such as a slow pre-discovery rise, a relatively broad light-curve peak showing a longer rise time (∼50 d), and a slower decline, along with a negligible change in the temperature around the peak (T ≤ 10^4 K). We suggest that SNhunt151 is the result of an outburst, or an SN explosion, within a dense circumstellar nebula, similar to those embedding some luminous blue variables like η Carinae and originating from past mass-loss events.STAMPAenArticle10.1093/mnras/sty0092-s2.0-85046010059000427345900082https://arxiv.org/pdf/1801.03040.pdfhttps://academic.oup.com/mnras/article/475/2/2614/47953092018MNRAS.475.2614EFIS/05 - ASTRONOMIA E ASTROFISICA