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RE: Supernova 2003bg
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First Ever Observed Hypernova?
Supernovae, or stars that undergo a massive explosion, are extremely important in physics. Other then that fact that exploding stars are intrinsically cool, supernovae have many practical scientific uses such as determining distances in the universe.

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Title: SN2003bg: a broad-lined Type IIb Supernova with Hydrogen
Authors: Paolo A. Mazzali (1,2,3,4), Jinsong Deng (5), Mario Hamuy (6), Ken'ichi Nomoto (7) ((1) Scuola Normale Superiore di Pisa, Italy, (2) INAF-OAPd, Italy, (3) MPA, Garching, Germany, (4) RESCEU, U. Tokyo, Japan, (5) NAO CAS, Beijing, China, (6) Astronomy Dept., U. Chile, (7) IPMU, U. Tokyo, Japan)

Models for the spectra and the light curve, 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 2003bg. Consistent fits to the light curve and the spectral evolution are obtained with an explosion that ejected ~ 4 M_sun of material with a kinetic energy of ~ 5 10^51 erg. A thin layer of hydrogen, comprising ~ 0.05 M_sun, is inferred to be present in the ejecta at the highest velocities (v >~ 9000 km/s), while a thicker helium layer, comprising ~ 1.25 M_sun, was ejected at velocities between 6500 and 9000 km/s. At lower velocities, heavier elements are present, including ~ 0.2 M_sun of 56Ni that shape the light curve and the late-time nebular spectra. These values suggest that the progenitor star had a mass of ~ 20-25 M_sun (comparable to, but maybe somewhat smaller than that of the progenitor of the XRF/SN 2008D). The rather broad-lined early spectra are the result of the presence of a small amount of material (~ 0.03 M_sun) at velocities > 0.1 c, which carries ~ 10 % of the explosion kinetic energy. No clear signatures of a highly aspherical explosion are detected.

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Title: 2003bg: The First Type IIb Hypernova
Authors: Mario Hamuy, Jinsong Deng, Paolo A. Mazzali, Nidia I. Morrell, Mark M. Phillips, Miguel Roth, Sergio Gonzalez, Joanna Thomas-Osip, Wojtek Krzeminski, Carlos Contreras, Jose Maza, Luis Gonzalez, Leonor Huerta, Gaston Folatelli, Ryan Chornock, Alexei V. Filippenko, S. E. Persson, W. L. Freedman, Kathleen Koviak, Nicholas B. Suntzeff, Kevin Krisciunas

Optical and near-infrared photometry and optical spectroscopy are reported for SN 2003bg, starting a few days after explosion and extending for a period of more than 300 days. Our early-time spectra reveal the presence of broad, high-velocity Balmer lines. The nebular-phase spectra, on the other hand, show a remarkable resemblance to those of Type Ib/c supernovae, without clear evidence for hydrogen. Near maximum brightness SN 2003bg displayed a bolometric luminosity comparable to that of other Type I hypernovae unrelated to gamma-ray bursts, implying a rather normal amount of 56Ni production (0.1-0.2 Msun) compared with other such objects. The bolometric light curve of SN 2003bg, on the other hand, is remarkably broad, thus suggesting a relatively large progenitor mass at the moment of explosion. These observations, together with the large value of the kinetic energy of expansion established in the accompanying paper (Mazzali et al. 2009), suggest that SN 2003bg can be regarded as a Type IIb hypernova.

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