Comparison between the first and second mass eruptions from progenitors of Type IIn supernovae

Abstract

Context. Some massive stars experience episodic and intense mass loss phases with fluctuations in the luminosity. Ejected material forms circumstellar matter around the star, and the subsequent core collapse results in a Type IIn supernova that is characterized by interaction between supernova ejecta and circumstellar matter. The energy source that triggers these mass eruptions and dynamics of the outflow have not been clearly explained. Moreover, the mass eruption itself can alter the density structure of the envelope and affect the dynamics of the subsequent mass eruption if these events are repeated. A large amount of observational evidence suggests multiple mass eruptions prior to core collapse. Aims. We investigate the density structure of the envelope altered by the first mass eruption and the nature of the subsequent second mass eruption event in comparison with the first event. Methods. We deposited extra energy at the bottom of the hydrogen envelope of 15 M⊙ stars twice and calculated the time evolution by radiation hydrodynamical simulation code. We did not deal with the origin of the energy source, but focused on the dynamics of repeated mass eruptions from a single massive star. Results. There are significant differences between the first and second mass eruptions in terms of the luminosity, color, and amount of produced circumstellar matter. The second eruption leads to a redder burst event in which the associated brightening phase lasts longer than the first. The amount of ejected matter is different even with the same deposited energy in the first and second event, but the difference depends on the density structure of the star. Conclusions. Upcoming high cadence and deep transient surveys will provide us a lot of pre-supernova activities, and some of which might show multi-peaked light curves. These should be interpreted taking the effect of density structure altered by the preceding outburst events into consideration.