We investigate the physical nature of blue cores in
early-type galaxies through the first multi-wavelength
analysis of a serendipitously discovered field
blue-nucleated spheroid in the background of the deep
ACS/WFC griz multicolor observations of the cluster Abell
1689. The resolved g-r, r-i and i-z color maps reveal
a prominent blue core identifying this galaxy as a
``typical'' case study, exhibiting variations of
0.5-1.0~mag in color between the center and the outer
regions, opposite to the expectations of redded metallicity
induced gradients in passively evolved ellipticals. From a
Magellan-Clay spectrum we secure the galaxy redshift at
z=0.624. We find a strong X-ray source coincident with the
spheroid galaxy. Spectral features and a high X-ray
luminosity indicate the presence of an AGN in the galaxy.
However, a comparison of the X-ray luminosity to a sample
derived from the Chandra Deep Field South displays Lx to
be comparable to Type~I/QSO galaxies while the optical flux
is consistent with a normal star-forming galaxy. We conclude
that the galaxy's non-thermal component dominates at
high-energy wavelengths while we associate the spheroid blue
light with the stellar spectrum of normal star-forming
galaxies. We argue about a probable association between the
presence of blue cores in spheroids and AGN activity.
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