We present the mass distribution in the central area of the cluster A1689 by fitting over 100 multiply lensed images with the non-parametric Strong Lensing Analysis Package ( SLAP , Diego et al .
2004 ) .
The surface mass distribution is obtained in a robust way finding a total mass of 0.25 \times 10 ^ { 15 } h ^ { -1 } M _ { \odot } within a 70 ” circle radius from the central peak .
Our reconstructed density profile fits well an NFW profile with small perturbations due to substructure and is compatible with the more model dependent analysis of Broadhurst et al .
( 2004a ) based on the same data .
Our estimated mass does not rely on any prior information about the distribution of dark matter in the cluster .
The peak of the mass distribution falls very close to the central cD and there is substructure near the center suggesting that the cluster is not fully relaxed .
We also examine the effect on the recovered mass when we include the uncertainties in the redshift of the sources and in the original shape of the sources .
Using simulations designed to mimic the data , we identify some biases in our reconstructed mass distribution .
We find that the recovered mass is biased toward lower masses beyond 1 arcmin ( 150 kpc ) from the central cD and that in the very center we may be affected by degeneracy problems .
On the other hand , we confirm that the reconstructed mass between 25 ” and 70 ” is a robust , unbiased estimate of the true mass distribution and is compatible with an NFW profile .