The multifaceted Type II-L supernova 2014G from pre-maximum to nebular phase

Journal
Date Issued
2016
Author(s)
Terreran, G.
•
Jerkstrand, A.
•
•
Smartt, S. J.
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Ochner, P.
•
•
Howell, D. A.
•
Morales-Garoffolo, A.
•
Harutyunyan, A.
•
Kankare, E.
•
Arcavi, I.
•
•
•
Hosseinzadeh, G.
•
Kangas, T.
•
•
•
•
Valenti, S.
•
Wiggins, P.
•
Yuan, F.
DOI
Abstract
We present multiband ultraviolet, optical, and near-infrared photometry, along with visual-wavelength spectroscopy, of supernova (SN) 2014G in the nearby galaxy NGC 3448 (25 Mpc). The early-phase spectra show strong emission lines of the high ionization species He II/N IV/C IV during the first 2-3 d after explosion, traces of a metal-rich circumstellar material (CSM) probably due to pre-explosion mass-loss events. These disappear by day 9 and the spectral evolution then continues matching that of normal Type II SNe. The post-maximum light curve declines at a rate typical of Type II-L class. The extensive photometric coverage tracks the drop from the photospheric stage and constrains the radioactive tail, with a steeper decline rate than that expected from the 56Co decay if γ-rays are fully trapped by the ejecta. We report the appearance of an unusual feature on the blue side of H α after 100 d, which evolves to appear as a flat spectral feature linking H α and the [O I] doublet. This may be due to interaction of the ejecta with a strongly asymmetric, and possibly bipolar CSM. Finally, we report two deep spectra at ∼190 and 340 d after explosion, the latter being arguably one of the latest spectra for a Type II-L SN. By modelling the spectral region around the [Ca II], we find a supersolar Ni/Fe production. The strength of the [O I] λλ6300,6363 doublet, compared with synthetic nebular spectra, suggests a progenitor with a zero-age main-sequence mass between 15 and 19 M☉.
Volume
462
Issue
1
Start page
137
Uri
Url
Issn Identifier
0035-8711
Ads BibCode
2016MNRAS.462..137T
Rights
open.access
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