Determining the Supernova Direction by its Neutrinos

Supernova neutrinos which arrive at the earth earlier than the light enable us the earliest determination of the direction of their emitter supernova. The theme of this paper is how accurately we can determine the supernova direction. We simulate supernova neutrino events at SuperKamiokande detector, using a realistic supernova model and several realistic neutrino oscillation models. In SuperKamiokande detector, the electron scattering reactions ($\nu+e^-\to \nu+e^-$) are highly correlated to the injected neutrinos' direction. These reactions, in the large background of isotropic inverse $\beta$-decay reactions ($\bar{\nu}_e+p\to e^++n$), are key to determine the supernova direction. As a result of our simulation we can restrict the supernova direction to be within a circle of radius $10^\circ$. Especially in several neutrino oscillation models, this accuracy is enhanced to $8^\circ$.