SN 2003bg: A BROAD-LINED TYPE IIb SUPERNOVA WITH HYDROGEN

Models for the spectra and the light curve (LC), in the photospheric as well as in the late nebular phase, are used to infer the properties of the very radio-bright, broad-lined type IIb supernova (SN) 2003bg. Consistent fits to the LC and the spectral evolution are obtained with an explosion that ejected approximate to 4 M-circle dot of material with a kinetic energy of approximate to 5 x 10(51) erg. A thin layer of hydrogen, comprising similar to 0.05 M-circle dot, is inferred to be present in the ejecta at the highest velocities (v greater than or similar to 9000 km s(-1)), while a thicker helium layer, comprising approximate to 1.25 M-circle dot, was ejected at velocities between 6500 and 9000 km s(-1). At lower velocities, heavier elements are present, including similar to 0.2 M-circle dot of Ni-56 that shape the LC and the late-time nebular spectra. These values suggest that the progenitor star had a mass of approximate to 20-25 M-circle dot, (comparable to, but may be somewhat smaller than that of the progenitor of the X-ray flashes/SN 2008D). The rather broad-lined early spectra are the result of the presence of a small amount of material (similar to 0.03 M-circle dot) at velocities >0.1c, which carries approximate to 10% of the explosion kinetic energy. No clear signatures of a highly aspherical explosion are detected.