  We consider the quantitative uniqueness properties for a parabolic type
equation $ u_t-\Delta u = w(x,t) \nabla u + v(x,t) u$, when $v \in L^{p_2}_{t}
L^{p_1}_x$ and $w \in L^{q_2}_{t} L^{q_1}_x$, with a suitable range for
exponents $p_1$, $p_2$, $q_1$, and $q_2$. We prove a strong unique continuation
property and provide a pointwise in time observability estimate.
