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Belfast, Ukraine

Tomasella L.,National institute for astrophysics | Cappellaro E.,National institute for astrophysics | Fraser M.,Queen University Belfast | Pumo M.L.,National institute for astrophysics | And 23 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

We present the one-year long observing campaign of SN 2012A which exploded in the nearby (9.8 Mpc) irregular galaxy NGC 3239. The photometric evolution is that of a normal Type IIP supernova, but the plateau is shorter and the luminosity not as constant as in other supernovae of this type. The absolute maximum magnitude, with MB = -16.23 ± 0.16 mag, is close to the average for SN IIP. Thanks also to the strong UV flux in the early phase, SN 2012A reached a peak luminosity of about 2 × 1042 erg s-1, which is brighter than those of other SNe with a similar 56Ni mass. The latter was estimated from the luminosity in the exponential tail of the light curve and found to be M(56Ni) = 0.011 ± 0.004M⊙, whichis intermediate between standard and faint SN IIP. The spectral evolution of SN 2012A is also typical of SN IIP, from the early spectra dominated by a blue continuum and very broad (~104 km s-1) Balmer lines, to the late-photospheric spectra characterized by prominent P-Cygni features of metal lines (Fe II, ScII, BaII, Ti II, CaII, NaI D). The photospheric velocity is moderately low, ~3 × 103 km s-1 at 50 d, for the low optical depth metal lines. The nebular spectrum obtained 394 d after the shock breakout shows the typical features of SNe IIP and the strength of the [O I] doublet suggests a progenitor of intermediate mass, similar to SN 2004et (~15M⊙). A candidate progenitor for SN 2012A has been identified in deep, pre-explosion K'-band Gemini North Near-InfraRed Imager and Spectrometerimages, and found to be consistent with a star with a bolometric magnitude -7.08 ± 0.36 (log L/L⊙ = 4.73 ± 0.14 dex). The magnitude of the recovered progenitor in archival images points towards a moderate-mass 10.5+4.5-2 M⊙ star as the precursor of SN 2012A. The explosion parameters and progenitor mass were also estimated by means of a hydrodynamical model, fitting the bolometric light curve, the velocity and the temperature evolutio. We found a best fit for a kinetic energy of 0.48 foe, an initial radius of 1.8 × 1013 cmand ejecta mass of 12.5M⊙. Even including the mass for the compact remnant, this appears fully consistent with the direct measurements given above. ©2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

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