Question: asymptotic expansion

Dear all

for a fixed x positive, I would like to find an asymptotic expansion of the following integral when n goes to infinity. 

int(exp(-n*(x*cosh(t)+t)), t = 0 .. infinity)

Maybe we can define 
f:=n->int(exp(-n*(x*cosh(t)+t)), t = 0 .. infinity);

asympt(f(n), n,2)
But doesn't work

Many thanks for your help 


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