Question: The limit at infinity with Maple

How to find the limit limit(u(x,t),t=infinity), where u(x,t) is the solution of the Cauchy problem:
pde:=diff(u(x,t),t)=diff(u(x,t),x,x)+exp(-t) with the initial condition
ic:=u(x,0)=arctan(x) ?

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