has a wide field of view and an angular resolution of 0.75$^\circ$, slightly larger than the disc of the Sun. The background arises primarily from the scattering of high-energy cosmic rays, producing $\gamma$’s which can arrive at the detector from within the Sun’s disc. Nonetheless, the limits obtained by Milagro for monochromatic sources are significant and reach up to 10 TeV. We exhibit the ensuing constraint on a contour plot of the $\gamma$-flux in Fig. \[fig-milagro\_lim\], which for characteristic scattering cross-sections, already imposes a significant constraint on the electromagnetic branching fractions. The primary flux limits obtained by Milagro are for monochromatic sources, while a monochromatic decay of the mediator as discussed above leads to a smoothed spectrum. Given that the background is a steeply-falling function of energy, while the expected signal is not, we adopt the Milagro bounds on monochromatic sources, weakening it by an order of magnitude in obtaining the bound in Fig. \[fig-milagro\_lim\].

In the near future, the Fermi-LAT detector, which is also able to observe the Sun [@lat] with an angular resolution about 10 times better than that of Milagro, should be able to improve on these limits and thus provide a very significant probe of secluded 