BENETTI, StefanoStefanoBENETTIChugai, N. N.N. N.ChugaiUtrobin, V. P.V. P.UtrobinCAPPELLARO, EnricoEnricoCAPPELLAROPatat, F.F.PatatPASTORELLO, AndreaAndreaPASTORELLOTURATTO, MassimoMassimoTURATTOCUPANI, GuidoGuidoCUPANINeuhäuser, R.R.NeuhäuserCaldwell, N.N.CaldwellPignata, G.G.PignataTOMASELLA, LinaLinaTOMASELLA2020-05-222020-05-2220160035-8711http://hdl.handle.net/20.500.12386/25079Spectrophotometry of SN 1996al carried out throughout 15 yr is presented. The early photometry suggests that SN 1996al is a linear Type II supernova, with an absolute peak of M<SUB>V</SUB> ∼ -18.2 mag. Early spectra present broad asymmetric Balmer emissions, with superimposed narrow lines with P-Cygni profile, and He I features with asymmetric broad emission components. The analysis of the line profiles shows that the H and He broad components form in the same region of the ejecta. By day +142, the Hα profile dramatically changes: the narrow P-Cygni profile disappears, and the Hα is fitted by three emission components that will be detected over the remaining 15 yr of the supernova (SN) monitoring campaign. Instead, the He I emissions become progressively narrower and symmetric. A sudden increase in flux of all He I lines is observed between 300 and 600 d. Models show that the SN luminosity is sustained by the interaction of low-mass (∼1.15 M<SUB>☉</SUB>) ejecta, expelled in a low kinetic energy (∼1.6 × 10<SUP>50</SUP> erg) explosion, with highly asymmetric circumstellar medium. The detection of Hα emission in pre-explosion archive images suggests that the progenitor was most likely a massive star (∼25 M<SUB>☉</SUB> ZAMS) that had lost a large fraction of its hydrogen envelope before explosion, and was hence embedded in a H-rich cocoon. The low-mass ejecta and modest kinetic energy of the explosion are explained with massive fallback of material into the compact remnant, a 7-8-M<SUB>☉</SUB> black hole.STAMPAenArticle10.1093/mnras/stv28112-s2.0-84963832420000372265200077https://academic.oup.com/mnras/article/456/3/3296/10943852016MNRAS.456.3296BFIS/05 - ASTRONOMIA E ASTROFISICA