Publication Date:
2013-08-18
Description:
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 M B = –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 x 10 42 erg s –1 , which is brighter than those of other SNe with a similar 56 Ni mass. The latter was estimated from the luminosity in the exponential tail of the light curve and found to be M( 56 Ni) = 0.011 ± 0.004 M , 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 (~10 4 km s –1 ) Balmer lines, to the late-photospheric spectra characterized by prominent P-Cygni features of metal lines (Fe ii , Sc ii , Ba ii , Ti ii , Ca ii , Na i D). The photospheric velocity is moderately low, ~3 x 10 3 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 (~15 M ). 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 $10.5_{-2}^{+4.5}\,{\rm M}_{\odot }$ 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 1.8 x 10 13 cm and ejecta mass of 12.5 M . Even including the mass for the compact remnant, this appears fully consistent with the direct measurements given above.
Print ISSN:
0035-8711
Electronic ISSN:
1365-2966
Topics:
Physics
Permalink