Publication Date:
2016-07-31
Description:
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 56 Co decay if -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 ] 6300,6363 doublet, compared with synthetic nebular spectra, suggests a progenitor with a zero-age main-sequence mass between 15 and 19 M .
Print ISSN:
0035-8711
Electronic ISSN:
1365-2966
Topics:
Physics
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