  The observed Y(4260)\to \gamma + X(3872) decay is a natural consequence of
the diquark-antidiquark description of Y and X resonances. In this note we
attempt an estimate of the transition rate, \Gamma_{\rm rad}, by a
non-relativistic calculation of the electric dipole term of a diquarkonium
bound state. We compute \Gamma_{\rm rad} for generic composition values of the
isospin of X and Y. Specializing to I=0 for X(3872), we find \Gamma_{\rm rad}=
496~keV for Y(4260) with I=0 and \Gamma_{\rm rad}= 179~keV for I=1. Combining
with BESIII data, we derive upper bounds to B(Y\to J/\Psi+\pi+\pi) and to
\Gamma(Y\to \mu^+ \mu^-). We expect to confront these results with forthcoming
data from electron-positron and hadron colliders.
