I am looking for approximations, or a closed form, if available, for  the sum  
$$S(n,a,b)=\sum_{1\leq x,y,\leq n}  \frac{x^a}{\mathrm{lcm}(x,y)^{b}},$$ 
where $\mathrm{lcm}(x,y)$ is the least common multiple of integers $x,y$ and $a,b$ are positive quantities. I am in particular interested in $a=b=1.$ For this case numerical evidence suggests
$$
S(n,1,1)=O( n \log n)
$$
may hold. In particular, I am wondering whether by using the technique in the answer to [this question][1] here, one might obtain (as $n \rightarrow \infty$), by letting $a,b\downarrow 1,$ an estimate in terms of zeta functions. In that question the upper bound
$$
S(n,0,b)\leq\frac{\zeta(b)^3}{\zeta(2b)},\quad b>1
$$
is derived by letting $n\rightarrow \infty.$
Any pointers,comments welcome.


  [1]: https://mathoverflow.net/questions/33600/double-sum-of-reciprocal-powers-of-integer-lcms