On regularity properties of Bessel flow

We study the differentiability of Bessel flow $\rho : x \to \rho ^x_t$, where $(\rho ^x_t)_{t\geq 0}$ is BES $^x(\delta$) process of dimension $\delta >1$ starting from $x$. For $\delta \geq 2$ we prove the existence of bicontinuous derivatives in P-a.s. sense at $x\geq 0$ and we study the asymptotic behaviour of the derivatives at $x=0$. For $1< \delta <2$ we prove the existence of a modification of Bessel flow having derivatives in probability sense at $x\geq 0$. We study the asymptotic behaviour of the derivatives at $t=\tau_0(x)$ where $\tau_0(x)$ is the first zero of $(\rho ^x_t)_{t\geq 0}$.