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Date and Time of the Query: 2019-04-24 T19:27:49 PDT
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For refcode 2016MNRAS.456.3296B:
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NED Abstract

Copyright by Royal Astronomical Society. 2016MNRAS.456.3296B The spectacular evolution of Supernova 1996al over 15 yr: a low-energy explosion of a stripped massive star in a highly structured environment Benetti, S.; Chugai, N. N.; Utrobin, V. P.; Cappellaro, E.; Patat, F.; Pastorello, A.; Turatto, M.; Cupani, G.; Neuhauser, R.; Caldwell, N.; Pignata, G.; Tomasella, L. Abstract. Spectrophotometry 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_V_ ~ -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 Halpha profile dramatically changes: the narrow P-Cygni profile disappears, and the Halpha 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_sun_) ejecta, expelled in a low kinetic energy (~1.6 x 10^50^ erg) explosion, with highly asymmetric circumstellar medium. The detection of Halpha emission in pre-explosion archive images suggests that the progenitor was most likely a massive star (~25 M_sun_ 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_sun_ black hole. Key words: supernovae: general
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