  Dark matter (DM) particles are predicted by several well motivated models to
yield Standard Model particles through self-annihilation that can potentially
be detected by astrophysical observations. In particular, the production of
charged particles from DM annihilation in astrophysical systems that contain
magnetic fields yields radio emission through synchrotron radiation and X-ray
emission through inverse Compton scattering of ambient photons. We introduce
RX-DMFIT, a tool used for calculating the expected secondary emission from DM
annihilation. RX-DMFIT includes a wide range of customizable astrophysical and
particle parameters and incorporates important astrophysics including the
diffusion of charged particles, relevant radiative energy losses, and magnetic
field modelling. We demonstrate the use and versatility of RX-DMFIT by
analyzing the potential radio and X-ray signals for a variety of DM particle
models and astrophysical environments including galaxy clusters, dwarf
spheroidal galaxies and normal galaxies. We then apply RX-DMFIT to a concrete
example using Segue I radio data to place constraints for a range of assumed DM
annihilation channels. For WIMP models with $M_{\chi} \leq 100$ GeV and
assuming weak diffusion, we find that the the leptonic $\mu^+\mu^-$ and
$\tau^+\tau^-$ final states provide the strongest constraints, placing limits
on the DM particle cross-section well below the thermal relic cross-section,
while even for the $b\bar{b}$ channel we find limits close to the thermal relic
cross-section. Our analysis shows that radio emission provides a highly
competitive avenue for dark matter searches.
