2003ApJ...598.1163M

Hydrodynamics and explosive nucleosynthesis in bipolar supernova explosions are examined to account for some peculiar properties of hypernovae as well as peculiar abundance patterns of metal-poor stars. The explosion is assumed to be driven by bipolar jets that are powered by accretion onto a central remnant. The energy injection rate by the jets is assumed to be proportional to the accretion rate, i.e., E{dot}_jet=αM{dot}c². We explore the features of the explosions with varying progenitors' masses and jet properties. The outcomes are different from conventional spherical models. (1) In the bipolar models, Fe-rich materials are ejected at high velocities along the jet axis, while O-rich materials occupy the central region, whose density becomes very high as a consequence of continuous accretion from the side. This configuration can explain some peculiar features in the light curves and the nebular spectra of hypernovae. (2) Production of ⁵⁶Ni tends to be smaller than in spherical thermal bomb models. To account for a large amount of ⁵⁶Ni observed in hypernovae, the jets should be initiated when the compact remnant mass is still smaller than 2-3 M_☉, or they should be very massive and slow. (3) Ejected isotopes are distributed as follows in order of decreasing velocities: ⁶⁴Zn, ⁵⁹Co, ⁵⁶Fe, ⁴⁴Ti, and ⁴He at the highest velocities; ⁵⁵Mn, ⁵²Cr, ³²S, and ²⁸Si at the intermediate velocities; and ²⁴Mg and ¹⁶O at the lowest velocities. (4) The abundance ratios (Zn, Co)/Fe are enhanced while the ratios (Mn, Cr)/Fe are suppressed. This can account for the abundance pattern of extremely metal-poor stars. These agreements between the models and observations suggest that hypernovae are driven by bipolar jets and have significantly contributed to the early Galactic chemical evolution.