Actor watch in Akka cluster

I create an Akka Cluster .Suppose on Node 1 I create an actor A and On Node2 I create another actor B.And in actor A I also watch actor B.
When Node2 become unreachable why actor A did not receive a Terminate message ?
Is there some best practise to fullfill something like this?Send an heatbeat?

The Terminated message will be triggered when the node hosting the actor is removed from the cluster, or if the actor itself is stopped.

Unreachability is only an observation by the cluster failure detector (using heartbeat messages) that the other node is, well, unreachable at the moment. It can come back and become reachable again eg because of a transient network problem. Therefore that signal is not suited for emitting Terminated.

To remove an unreachable node from the cluster it must first be downed, which is a final decision. That is typically done using a downing strategy. See documentation.

Thanks for replying.