Padova-Asiago Supernova Group

The spectacular evolution of Supernova 1996al over 15 years: a low energy explosion of a stripped massive star in a highly structured environment
Benetti, S., et al. MNRAS in press
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Spectrophotometry of SN 1996al carried out throughout 15 years is presented. The early photometry suggests that SN 1996al is a Linear type-II supernova, with an absolute peak of MV ~18.2 mag. Early spectra present broad, asymmetric Balmer emissions, with super-imposed 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 yrs of the 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 days. Models show that the supernova luminosity is sustained by the interaction of low mass (~1.15 Msun) ejecta, expelled in a low kinetic energy (~ 1.6 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 Msun 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 Msun black hole.

sn galaxy RA DEC discoverer type redshift ref class fits
anonymous 03:10:34.50 +04:16:10.9 ASAS-SN Ia 0.023166 ATEL
CGCG 336-41 14:06:44.37 +71:53:15.3 ASAS-SN Ia 0.034 ATEL
UGC 3376 05:54:40.63 +15:10:27.4 LOSS II 0.013139 ATEL
PGC 22658 08:04:16.02 +61:33:42.70 Ciabattari II-P 0.03 ATEL
UGC 5434 10:05:13.74 +21:27:23.1 M. Peoples,E. Weinberg,R. Post,J. Newton,T.Puckett II 0.018613 ATEL