ASASSN-15no: the Supernova that plays hide-and-seek. Issue 1 (27th February 2018)

• Record Type: Journal Article
• Authors: Benetti, S; Zampieri, L; Pastorello, A; Cappellaro, E; Pumo, M L; Elias-Rosa, N; Ochner, P; Terreran, G; Tomasella, L; Taubenberger, S; Turatto, M; Morales-Garoffolo, A; Harutyunyan, A; Tartaglia, L
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 476:Issue 1(2018)
• Page Start: 261
• Page End: 270
• Publication Date: 2018-02-27
• Subjects: supernovae: general -- supernovae: individual: ASASSN-15no; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/sty166
• Languages: English
• ISSNs: 0035-8711

Abstract

Abstract: We report the results of our follow-up campaign of the peculiar supernova ASASSN-15no, based on optical data covering ∼300 d of its evolution. Initially the spectra show a pure blackbody continuum. After few days, the HeI λλ 5876 transition appears with a P-Cygni profile and an expansion velocity of about 8700 km s −1 . Fifty days after maximum, the spectrum shows signs typically seen in interacting supernovae. A broad (FWHM ∼ 8000 km s −1 ) Hα becomes more prominent with time until ∼150 d after maximum and quickly declines later on. At these phases Hαstarts to show an intermediate component, which together with the blue pseudo-continuum are clues that the ejecta begin to interact with the circumstellar medium (CSM). The spectra at the latest phases look very similar to the nebular spectra of stripped-envelope SNe. The early part (the first 40 d after maximum) of the bolometric curve, which peaks at a luminosity intermediate between normal and superluminous supernovae, is well reproduced by a model in which the energy budget is essentially coming from ejecta recombination and 56 Ni decay. From the model, we infer a mass of the ejecta Mej = 2.6 M⊙ ; an initial radius of the photosphere R0 = 2.1 × 10 14 cm; and an explosion energy Eexpl = 0.8 × 10 51 erg. A possible scenario involves a massive and extended H-poor shell lost by the progenitor star a few years before explosion. The shell is hit, heated, and accelerated by the supernova ejecta. The accelerated shell+ejecta rapidly dilutes, unveiling the unperturbed supernova spectrum below. The outer ejecta start to interact with a H-poor external CSM lost by the progenitor system about 9–90 yr before the explosion.