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Supernova 2007Y

Title: The He-rich core-collapse supernova 2007Y: Observations from X-ray to Radio Wavelengths
Authors: Maximilian Stritzinger, Paolo Mazzali, Mark M. Phillips, Stefan Immler, Alicia Soderberg, Jesper Sollerman, Luis Boldt, Jonathan Braithwaite, Peter Brown, Christopher R. Burns, Carlos Contreras, Ricardo Covarrubias, Gaston Folatelli, Wendy L. Freedman, Sergio Gonzalez, Mario Hamuy, Wojtek Krzeminski, Barry F. Madore, Peter Milne, Nidia Morrell, S. E. Persson, Miguel Roth, Mathew Smith, Nicholas B. Suntzeff

A detailed study spanning approximately a year has been conducted on the Type Ib supernova 2007Y. Imaging was obtained from X-ray to radio wavelengths, and a comprehensive set of multi-band (w2m2w1u'g'r'i'UBVYJHKs) light curves and optical spectroscopy is presented. A virtually complete bolometric light curve is derived, from which we infer a (56)Ni-mass of 0.06 M_sun. The early spectrum strongly resembles SN 2005bf and exhibits high-velocity features of CaII and H_alpha; during late epochs the spectrum shows evidence of a ejecta-wind interaction. Nebular emission lines have similar widths and exhibit profiles that indicate a lack of major asymmetry in the ejecta. Late phase spectra are modelled with a non-LTE code, from which we find (56)Ni, O and total-ejecta masses (excluding He) to be 0.06, 0.2 and 0.42 M_sun, respectively, below 4,500 km/s. The (56)Ni mass confirms results obtained from the bolometric light curve. The oxygen abundance suggests the progenitor was most likely a ~3.3 M_sun He core star that evolved from a zero-age-main-sequence mass of 10-13 M_sun. The explosion energy is determined to be ~10^50 erg, and the mass-loss rate of the progenitor is constrained from X-ray and radio observations to be <~10^-6 M_sun/yr. SN 2007Y is among the least energetic normal Type Ib supernovae ever studied.

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