Speaker: Kohki Uno
Light-Curve Modeling for Rapid-Evolving Transients
Recently, thanks to new generation surveys (e.g., ZTF), some new-class transients have been discovered. The surveys reveal the hidden natures of astronomical transients. Fast Blue Optical Transients (FBOTs) are one of the most peculiar new-class transients, which show rapid-evolving light curves and high peak luminosity. FBOTs have different observational properties, which cannot be reproduced by a supernova-like instantaneous explosion. Assuming that a continuous outflow like a stellar wind is injected from a central system, we propose a wind-driven model to explain the peculiar transients (Uno&Maeda 2020a). We apply the model to AT2018cow, which is the most famous FBOT sample. The wind model suggests that AT2018cow is powered by the large mass-loss rates (> ~10 M_sun/yr), and the characteristic radii of ~1e13 cm for the launch of the wind. The model predicts characteristic photometric and spectral features. We then suggest that AT2018cow may be either a tidal disruption event or a BH-forming failed supernova. In this talk, I will introduce the wind-driven model and discuss my recent work on applying the model to the initial-rising phase of FBOTs.
Speaker: Mao Ogawa
Systematic Investigation of very Early-phase Spectra of Type Ia Supernovae
It has been widely accepted that Type Ia supernovae (SNe Ia) are thermonuclear explosions of a CO white dwarf in a binary system. However, the nature of the progenitor systems and explosion mechanisms are still unclarified. Thanks to the recent technological development of transient observation, we now detect them shortly after the explosion, followed by rapid spectroscopic observations. In this study, by modeling very early-phase spectra of SNe Ia, we try to constrain the explosion models of SNe Ia. By using one-dimensional Monte Carlo radiation transfer code, TARDIS, we estimate the density and composition structures of the outermost ejecta of SNe Ia. We find that the photospheric velocity of normal-velocity type supernovae (NV SNe) is ~15000 [km/s], but outer velocity, which corresponds to the velocity to which carbon burning extends, is divided into two types, ~20000 [km/s] and 25000 [km/s]. Furthermore, the former tends to have a higher density than the latter. For high-velocity type supernovae (HV SNe) and 1999aa-like SNe, on the other hand, photospheric velocity is higher, ~20000 [km/s]. These two types can be divided by the photospheric density and composition structure; the density of HV SNe is higher than that of 1999aa-like SNe. We also show the composition structures are divided into two groups; one dominated by the carbon burning layer (with little/no unburnt C+O layer), and the other dominated by the unburnt C+O layer. The former belongs to NV SNe with low density and 1999aa-like SNe, and the latter includes NV SNe with high density and HV SNe. These two sequences may be associated with different progenitor channels.
