  The eXciting Dark Matter (XDM) model was proposed as a mechanism to
efficiently convert the kinetic energy (in sufficiently hot environments) of
dark matter into e+e- pairs. The standard scenario invokes a doublet of nearly
degenerate DM states, and a dark force to mediate a large upscattering cross
section between the two. For heavy ($\sim TeV$) DM, the kinetic energy of WIMPs
in large (galaxy-sized or larger) halos is capable of producing low-energy
positrons. For lighter dark matter, this is kinematically impossible, and the
unique observable signature becomes an X-ray line, arising from $\chi \chi
\rightarrow \chi^* \chi^*$, followed by $\chi^* \rightarrow \chi \gamma$. This
variant of XDM is distinctive from other DM X-ray scenarios in that it tends to
be most present in more massive, hotter environments, such as clusters, rather
than nearby dwarfs, and has different dependencies from decaying models. We
find that it is capable of explaining the recently reported X-ray line at 3.56
keV. For very long lifetimes of the excited state, primordial decays can
explain the signal without the presence of upscattering. Thermal models
freeze-out as in the normal XDM setup, via annihilations to the light boson
$\phi$. For suitable masses the annihilation $\chi \chi \rightarrow \phi \phi$
followed by $\phi \rightarrow SM$ can explain the reported gamma-ray signature
from the galactic center. Direct detection is discussed, including the
possibility of explaining DAMA via the "Luminous" dark matter approach. Quite
generally, the proximity of the 3.56 keV line to the energy scale of DAMA
motivates a reexamination of electromagnetic explanations. Other signals,
including lepton jets and the modification of cores of dwarf galaxies are also
considered.
