Interacting supernova remnants: tunnels in the sky.

Two-dimensional calculations of near-surface, atmospheric nuclear fireballs and interacting supernova remnants (SNRs) are presented. The fireball calculations demonstrate the ability of the LASL program YAQUI to reproduce known time-dependent evolution of fireballs. The SNR calculation describes the interaction of two remnants aged 6400 and 32000 years. A dense plug is formed which separates the two cavity volumes. The combined volume of the cavities is 80% of the sum of the volumes of two isolated remnants but exceeds the union volume of two overlapping, noninteracting remnants. The resultant tunnel fraction is then greater than the value derived from simple considerations.