Peculiar chemical abundances in the starburst galaxy M82 and hypernova nucleosynthesis

X-ray observations have shown that the chemical abundance in the starburst galaxy M82 is quite rich in Si and S compared to oxygen. Such an abundance pattern cannot be explained with any combination of conventional Type I and II supernova yields. In addition, the energy-to-heavy-element mass ratio of the observed hot plasma is much higher than the value resulting from normal supernovae. We calculate abundances for explosive nucleosynthesis in core-collapse hypernovae and show that the abundance pattern and the large ratio between the energy and the heavy-element mass can be explained with hypernova nucleosynthesis. Such hypernova explosions are expected to occur for stars more massive than greater than or similar to20-25 M., and they likely dominate the starburst, because the time since the starburst in M82 is estimated to be as short as similar to10(6)-10(7) yr. We also investigate pair-instability supernovae (similar to150-300 M.) and conclude that the energy-to-heavy-element mass ratio in these supernovae is too small to explain the observation.