Speaker
Description
The radiation reprocessing model, in which an optically-thick layer or outflow absorbs the high-energy emission from a central source and re-emits in longer wavelengths, has been frequently invoked to explain some optically bright transients such as tidal disruption events (TDEs) and fast blue optical transients (FBOTs).Previous studies on this model did not take into account either the time evolution of the radiation signature or the frequency-dependent opacity. We study the radiative reprocessing in a time-dependent, steady-state and spherical outflow composed of pure hydrogen gas. Frequency-dependent bound-free, free-free, bound-bound and electron scattering opacities are considered. We present the analytical and numerical results of the emitted spectrum and the light curve. The results show that although the outflow is highly ionized, the bound-free transition in the outflow cannot be neglected due to its large cross-section. The results also show that the emitted spectrum has a significant extension in the NIR band, and evolves as $L_{\nu} \propto \nu^{0.5}$. The model predicts light curves at different wavelengths. We discuss the effects of the injected luminosity, and the mass and velocity of the outflow on the results. We apply our model to the typical FBOT AT2018cow.
