2013MNRAS.434.1636T

We present the one-year long observing campaign of SN 2012A which exploded in the nearby (9.8Mpc) 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±0.16mag, 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 2x10⁴² erg/s, 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_☉, which is 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) Balmer lines, to the late-photospheric spectra characterized by prominent P-Cygni features of metal lines (Feii, Scii, Baii, Tiii, Caii, Nai D). The photospheric velocity is moderately low, ∼ 3x10³km/s at 50d, for the low optical depth metal lines. The nebular spectrum obtained 394d after the shock breakout shows the typical features of SNe IIP and the strength of the [Oi] 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 Spectrometer images, 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_-2^+4.5 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 evolution. We found a best fit for a kinetic energy of 0.48 foe, an initial radius of 1.8x10¹³ cm and ejecta mass of 12.5M_☉. Even including the mass for the compact remnant, this appears fully consistent with the direct measurements given above.