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 Ni-56 mass of 0.06 M-circle dot. The early spectrum strongly resembles SN 2005bf and exhibits high- velocity features of Ca II and H alpha; 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 Ni-56, O, and total-ejecta masses (excluding He) to be 0.06, 0.2, and 0.42 M-circle dot, respectively, below 4500 km s(-1). The Ni-56 mass confirms results obtained from the bolometric light curve. The oxygen abundance suggests that the progenitor was most likely a approximate to 3.3 M-circle dot He core star that evolved from a zero-age-main-sequence mass of 10-13 M-circle dot. The explosion energy is determined to be approximate to 10(50) erg, and the mass-loss rate of the progenitor is constrained from X-ray and radio observations to be less than or similar to 10(-6) M-circle dot yr(-1). SN 2007Y is among the least energetic normal Type Ib SNe ever studied.