Detectability of supernova emission varies with viewing angle

While supernovae – the result of stars collapsing under their own gravity – are well described and understood, it is less clear under which circumstances these events are also associated with the emission of relativistic jets, observed as Gamma-Ray Bursts. Since these jets are launched along the poles of the Black Holes formed in supernovae, their detection is orientation-dependent. In a recent publication (The Astrophysical Journal 759), CAASTRO’s former PhD student Sharon Rapoport, her ANU supervisors, and international colleagues simulated a range of different scenarios to take the mass and composition of the star, viewing angle of the observer (orientation), and timescale of the supernova into account to predict the detectability of the jets.

Their simulations recreate 50 days after the collapse and show that supernovae progress differently depending on their initial composition (which affects density) and assumed expansion velocities (which are faster along the poles than along the equator). The team also found a consistent relationship between light curve properties and the observer’s orientation. Light curves peaked around 20 days after the supernova, but pre-peak light curves were brighter for observing lines of sight aligned with the pole-axis.  The simulations also revealed a rapid colour evolution from blue to red, corresponding to higher velocities by lighter elements being transformed into metal.

Having identified the viewing angle as a key factor in analysing light curves, these simulations now caution us in our estimates of energy and mass being ejected in supernovae. The results also provide a guide as to what properties we should be closely examining in future observations of supernovae and associated emissions, to further improve our models and understanding of these extreme physical processes.

 

Publication details:

S. Rapoport, S. A. Sim, K. Maeda, M. Tanaka, M. Kromer, B. P. Schmidt, K. Nomoto in ApJ 759: “A theoretical color-velocity correlation for Supernovae associated with Gamma-Ray Bursts