SN 2015as: a low-luminosity Type IIb supernova without an early light-curve peak
Date Issued
2018
Author(s)
Gangopadhyay, Anjasha
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Misra, Kuntal
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Sahu, D. K.
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•
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Singh, Mridweeka
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Dastidar, Raya
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Srivastav, S.
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Ochner, P.
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Brown, Peter J.
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Anupama, G. C.
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Kumar, Brajesh
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Kumar, Brijesh
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Pandey, S. B.
Abstract
We present results of the photometric (from 3 to 509 d post-explosion) and spectroscopic (up to 230 d post-explosion) monitoring campaign of the He-rich Type IIb supernova (SN) 2015as. The (B − V) colour evolution of SN 2015as closely resemble those of SN 2008ax, suggesting that SN 2015as belongs to the SN IIb subgroup that does not show the early, short-duration photometric peak. The light curve of SN 2015as reaches the B-band maximum about 22 d after the explosion, at an absolute magnitude of −16.82 ± 0.18 mag. At ∼75 d after the explosion, its spectrum transitions from that of a SN II to a SN Ib. P Cygni features due to He i lines appear at around 30 d after explosion, indicating that the progenitor of SN 2015as was partially stripped. For SN 2015as, we estimate a 56Ni mass of ∼0.08 M☉ and ejecta mass of 1.1-2.2 M☉, which are similar to the values inferred for SN 2008ax. The quasi-bolometric analytical light-curve modelling suggests that the progenitor of SN 2015as has a modest mass (∼0.1 M☉), a nearly compact (∼0.05 × 1013 cm) H envelope on top of a dense, compact (∼2 × 1011 cm) and a more massive (∼1.2 M☉) He core. The analysis of the nebular phase spectra indicates that ∼0.44 M☉ of O is ejected in the explosion. The intensity ratio of the [Ca ii]/[O i] nebular lines favours either a main-sequence progenitor mass of ∼15 M☉ or a Wolf-Rayet star of 20 M☉.
Volume
476
Issue
3
Start page
3611
Issn Identifier
0035-8711
Ads BibCode
2018MNRAS.476.3611G
Rights
open.access
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