  Abell 1689 is a well studied cluster of galaxies and one of the largest
gravitational lens systems ever observed. We have obtained a reconstruction of
the cluster Abell 1689 using Grale, a free-form lens inversion method that
relies exclusively on the multiple image data. Non-inclusion of any data
related to cluster member galaxies ensures an unbiased measure of the mass
distribution, which is the most notable feature of free-form methods like
Grale. We used two different sets of multiple image systems from the available
strong lensing data - one containing only the secure systems (107 images), and
the other containing all available systems, only excluding some very non-secure
systems (151 images). For the very well-constrained central $\sim$100 kpc
region of the cluster we made detailed comparison of the Grale reconstructed
lensing mass and stellar mass retrieved by the Spectral Energy Distribution
(SED) fitting software FAST++. We found a light-unaccompanied mass peak in this
region, whose existence, while tentative, is favored by the distribution of
nearby images that are local maxima in the Fermat potential. However, further
tests, using different methodologies are needed to confirm the reality of this
feature. If it shown to be real, this light-unaccompanied mass peak is
consistent with dark matter self-interaction cross-section $\sigma \lesssim
1$cm$^2$/g, while being in tension with larger cross-sections.
