Constraints on dark matter models from a Fermi LAT search for high-energy cosmic-ray electrons from the Sun

During its first year of data taking, the Large Area Telescope (LAT) onboard the Fermi Gamma-Ray Space Telescope has collected a large sample of high-energy cosmic-ray electrons and positrons (CREs). We present the results of a directional analysis of the CRE events, in which we searched for a flux excess correlated with the direction of the Sun. Two different and complementary analysis approaches were implemented, and neither yielded evidence of a significant CRE flux excess from the Sun. We derive upper limits on the CRE flux from the Sun’s direction, and use these bounds to constrain two classes of dark matter models which predict a solar CRE flux: (1) models in which dark matter annihilates to CREs via a light intermediate state, and (2) inelastic dark matter models in which dark matter annihilates to CREs.

Figure 1

Differential flux asymmetry between real and fake Sun evaluated in cones with angular radii $\Delta \Theta =30°$ (top left panel), 45° (top right panel), 60° (bottom left panel), and 90° (bottom right panel). The fluxes are multiplied by $E^3$ (the energy values correspond to the bin centers) since the energy spectrum of CREs is approximately proportional to $E^{-3}$ in this energy range. Only statistical error bars are shown.

Figure 2

Statistical upper limits at confidence levels of 68% (dotted lines), 95% (dashed lines), and 99% (continuous lines) for the CRE flux asymmetry between real and fake Sun, evaluated in cones with angular radii $\Delta \Theta =30°$ (top left panel), 45° (top right panel), 60° (bottom left panel), and 90° (bottom right panel).

Figure 3

Differential flux asymmetry between real and simulated events from the Sun evaluated in cones with angular radii $\Delta \Theta =30°$ (top left panel), 45° (top right panel), 60° (bottom left panel), and 90° (bottom right panel). Only statistical error bars are shown.

Figure 4

Statistical upper limits at confidence levels of 68% (dotted lines), 95% (dashed lines), and 99% (continuous lines) for the CRE fluxes from the Sun, evaluated in cones with angular radii $\Delta \Theta =30°$ (top left panel), 45° (top right panel), 60° (bottom left panel), and 90° (bottom right panel).

Figure 5

Angular power spectra for different minimum energies: 60 GeV (top left panel), 100 GeV (top right panel), 200 GeV (bottom left panel), 500 GeV (bottom right panel). The points show the quantities ${\widehat{C}}_l-C_N$. The dashed lines and the continuous lines show, respectively, the $3\sigma$ and $5\sigma$ intervals for the probability distribution of the white noise.

Figure 6

Constraints on DM annihilation to $e^{+}{e}^{-}$ via an intermediate state, from solar CRE flux upper limits. Solar capture of DM is assumed to take place via spin-independent scattering. The constraints obtained for three values of the decay length $L$ of the intermediate state are shown. Models above the curves exceed the solar CRE flux upper limit at 95% CL for a 30° ROI centered on the Sun.

Figure 7

Constraints on DM parameters for annihilation to $e^{+}{e}^{-}$ via an intermediate state as in Fig. 6, except assuming solar capture by spin-dependent scattering.

Figure 8

Constraints on iDM model parameters for three values of the mass splitting $\delta$. Models above the curves produce a solar CRE flux that exceeds the 95% CL flux upper limit for a 30° ROI centered on the Sun in one or more energy bins.