Dark matter discovery potential of the Advanced Particle-Astrophysics Telescope

Gamma-ray observations of Milky Way dwarf galaxies have been used to place stringent constraints on the dark matter’s annihilation cross section. In this paper, we evaluate the sensitivity of the proposed Advanced Particle-Astrophysics Telescope (APT) to dark matter in these systems, finding that such an instrument would be capable of constraining thermal relics with masses as large as $m_X\sim 600\mathrm{GeV}$. Furthermore, in dark matter scenarios motivated by the observed Galactic Center gamma-ray excess, we predict that APT would detect several dwarf galaxies with high significance. Such observations could be used to test the predicted proportionality between the gamma-ray fluxes and $J$-factors of individual dwarf galaxies, providing us with an unambiguous test of the origin of the Galactic Center excess.

Figure 1

A comparison of the constraints on the dark matter annihilation cross section (to $b\overline{b}$) attained from four years of simulated (left) or real (right) Fermi data, from the directions of 15 dwarf galaxies. The solid lines and the surrounding green and yellow bands denote the median constraint and the range of constraints attained in 68% and 95% of the simulated realizations, respectively. In the right frame, we show the results from Ref. [34], which were derived from four years of real Fermi data. The similarity between the simulated and real constraints demonstrates that our model provides an adequate description of the relevant backgrounds.

Figure 2

The projected constraints on the dark matter annihilation cross section (to $b\overline{b}$ or ${\tau }^{+}{\tau }^{-}$) for ten years of APT data from the directions of 30 Milky Way dwarf galaxies (see Table 1). The solid lines and the surrounding green and yellow bands denote the median constraint and the range of constraints attained in 68% and 95% of the simulated realizations, respectively. The dashed curve is the annihilation cross section predicted for a dark matter candidate that is a (velocity-independent) thermal relic [20], while the dot-dashed line is the current constraint from Fermi data, as presented in Ref. [36].

Figure 3

As in Fig. 2 but for other annihilation channels. These projected constraints are based on ten years of simulated APT data from the directions of 30 Milky Way dwarf galaxies (see Table 1). The solid lines and the surrounding green and yellow bands denote the median constraint and the range of constraints attained in 68% and 95% of the simulated realizations, respectively. The dashed curve is the annihilation cross section predicted for a dark matter candidate that is a (velocity-independent) thermal relic [20].

Figure 4

The projected ability of APT (with ten years of data) to measure the dark matter mass and annihilation cross section in a scenario with $m_X=45\mathrm{GeV}$ and $⟨\sigma v⟩=2\times {10}^{-26}{\mathrm{cm}}^3/\mathrm{s}$ (to $b\overline{b}$), as motivated by the Galactic Center gamma-ray excess. The star and surrounding contours represent the best-fit value and the 1, 3, and $5\sigma$ confidence intervals, respectively. In such a scenario, we project that APT could exclude the null hypothesis at a level of $2\mathrm{\Delta }\ln \mathcal{L}\approx -200$, corresponding to a significance of $14\sigma$.

Figure 5

The projected ability of APT (with ten years of data) to measure the gamma-ray fluxes (integrated above 0.1 GeV) from individual dwarf galaxies in a scenario with $m_X=45\mathrm{GeV}$ and $⟨\sigma v⟩=2\times {10}^{-26}{\mathrm{cm}}^3/\mathrm{s}$ (to $b\overline{b}$), as motivated by the Galactic Center gamma-ray excess. These fluxes are compared to the $J$-factors of the dwarfs, as integrated within a radius of 0.5°. These results were attained in a single (but representative) realization of our simulation, showing each dwarf that was detected with a significance of $2\sigma$ or higher. Such a dataset would allow us to test whether the gamma-ray fluxes from dwarf galaxies are proportional to the corresponding $J$-factors, providing an unambiguous test of dark matter interpretations of the Galactic Center gamma-ray excess.