The he-rich core-collapse supernova 2007Y: Observations from X-ray to radio wavelengths

A detailed study spanning approximately a year has been conducted on the Type Ib supernova (SN) 2007Y. Imaging was obtained from X-ray to radio wavelengths, and a comprehensive set of multi-band (w2m2w1u′g′ r′i′UBVYJHK_s) light curves and optical spectroscopy is presented. A virtually complete bolometric light curve is derived, from which we infer a ⁵⁶Ni mass of 0.06 M_⊙. The early spectrum strongly resembles SN 2005bf and exhibits high-velocity features of Ca ii and Hα; during late epochs the spectrum shows evidence of an 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 modeled with a non-LTE code, from which we find ⁵⁶Ni, O, and total-ejecta masses (excluding He) to be 0.06, 0.2, and 0.42 M_⊙, respectively, below 4500 km s^-1. The ⁵⁶Ni mass confirms results obtained from the bolometric light curve. The oxygen abundance suggests that the progenitor was most likely a ≈3.3 M_⊙ He core star that evolved from a zero-age-main-sequence mass of 10-13 M_⊙. The explosion energy is determined to be ≈10⁵⁰ erg, and the mass-loss rate of the progenitor is constrained from X-ray and radio observations to be ≤ 10^-6 M_⊙ yr^-1. SN 2007Y is among the least energetic normal Type Ib SNe ever studied.