Well-posedness and Continuity Properties of the Fornberg_Whitham equation in Besov space $B_{\mathrm{\infty },1}^1(\mathbb{R})$

For the Fornberg-Whitham equation, the local well-posedness in the critical Besov space $B_{p,1}^{1+\frac{1}{p}}(\mathbb{R})$ with $1\le p<\mathrm{\infty }$ has been studied in (Guo, Nonlinear Anal. RWA., 2023). However, for the endpoint case $p=\mathrm{\infty }$, whether it is locally well-posed or ill-posed in $B_{\mathrm{\infty },1}^1(\mathbb{R})$ is still unknown. In this paper, we prove that the Fornberg-Whitham equation is well-posed in the critical Besov space $B_{\mathrm{\infty },1}^1(\mathbb{R})$ with solutions depending continuously on initial data, which is different from that of the Camassa-Holm equation (Guo et al., J. Differ. Equ., 2022). In addition, we show that this dependence is sharp by showing that the solution map is not uniformly continuous on the initial data.