Quantitative study of the AMS-02 electron/positron spectra: Implications for pulsars and dark matter properties

The Alpha Magnetic Spectrometer (AMS-02) has just published the unprecedentedly precise measurement of the cosmic electron and positron spectra. In this paper, we try to give a quantitative study on the AMS-02 results by a global fitting to the electron and positron spectra, together with the updated positron fraction data. The Markov chain Monte Carlo algorithm is adopted to do the fitting. The primary electron spectrum and the parameters for pulsars or dark matter that contribute extra positrons are determined simultaneously. We find that there is a hardening of the primary electron spectrum at $\sim 60\mathrm{GeV}$. With such a new feature at the background spectrum, both the pulsars and dark matter can explain the AMS-02 results very well. The dark matter scenario shows a drop at the positron fraction at $\sim 300\mathrm{GeV}$ but suffers very strong constraints from Fermi $\gamma$-ray observations. The fitting results also suggest that the propagation model with convection may be more favored by the lepton data than the reacceleration model.

Figure 1

The $\mathrm{B}/\mathrm{C}$ ratio (left) and ${}^{10}\mathrm{Be}/{}^9\mathrm{Be}$ ratio (right) for the corresponding parameters shown in Table 1, compared with the data. The bands show the 95% confidence ranges. The $\mathrm{B}/\mathrm{C}$ data are from AMS-02 [38] and ACE [46], and the ${}^{10}\mathrm{Be}/{}^9\mathrm{Be}$ data are from experiments ACE [47], Balloon [48, 49, 50], IMP7&8 [51], ISEE3-HKH [52], ISOMAX [53], Ulysses-HET [54], and Voyager [55].

Figure 2

The fluxes of protons for the corresponding parameter shown in Table 2, compared with the preliminary data from AMS-02 [38]. The bands delimit the regions of the 95% confidence level.

Figure 3

The expected results for the best-fitting parameters in the DR scenario with one break of the primary electron injection spectrum. Top left: positron fraction $e^{+}/(e^{+}+e^{-})$; top right: electron plus positron flux $e^{+}+e^{-}$; bottom left: electron flux $e^{-}$; and bottom right: positron flux $e^{+}$. The thin red, green, and thick blue curves represent the pulsar, DM annihilation into ${\mu }^{+}{\mu }^{-}$, and ${\tau }^{+}{\tau }^{-}$ final states, respectively. Different line styles represent different components as labeled.

Figure 4

Same as Fig. 3 but for the DC propagation scenario.

Figure 5

The same as Fig. 3 but for the background model with two breaks in the electron injection spectrum.

Figure 6

The same as Fig. 5 but for the DC propagation scenario.

Figure 7

The one- and two-dimensional distributions of part of the parameters for DM annihilation into the ${\mu }^{+}{\mu }^{-}$ channel. The background electrons have two breaks, and the propagation model is DR. The contours in the two-dimensional plots denote the 68.3%, 95.5%, and 99.7% confidence levels from inside to outside.

Figure 8

The same as Fig. 7 but for the DC propagation scenario.

Figure 9

Comparison of the positron spectra between the DC scenario (thin red) and DR scenario (green) with an extra source component from DM annihilation into the ${\mu }^{+}{\mu }^{-}$ final state.

Figure 10

$1\sigma$ and $2\sigma$ confidence regions in the $m_{\chi }-⟨\sigma v⟩$ plane, together with the exclusion lines from Fermi $\gamma$-ray observations [83, 84]. The left panel is for the $\mu$ channel, while the right panel is for the $\tau$ channel. Thin red contours are for DC scenario, and green ones are for the DR scenario. The dashed regions are for the case with only one break in the primary electron injection spectrum, while the solid regions are for those with an additional break.