Galactic diffuse gamma rays --- recalculation based on the new measurements of cosmic electron spectrum

In this work, we revisit the all-sky Galactic diffuse $gamma$-ray emission taking into account the new measurements of cosmic ray electron/positron spectrum by PAMELA, ATIC and Fermi, which show excesses of cosmic electrons/positrons beyond the expected fluxes in the conventional model. Since the origins of the extra electrons/positrons are not clear, we consider three different scenarios to account for the excesses: the astrophysical sources such as the Galactic pulsars, dark matter decay and annihilation. Further, new results from Fermi-LAT of the (extra-)Galactic diffuse $gamma$-ray are adopted. The background cosmic rays without the new sources give lower diffuse $gamma$ rays compared to Fermi-LAT observation, which is consistent with previous analysis. The scenario with astrophysical sources predicts diffuse $gamma$-rays with little difference with the background. The dark matter annihilation models with $tau^{pm}$ final state are disfavored by the Fermi diffuse $gamma$-ray data, while there are only few constraints on the decaying dark matter scenario. Furthermore, these is always a bump at higher energies ($sim$ TeV) of the diffuse $gamma$-ray spectra for the dark matter scenarios due to final state radiation. Finally we find that the Fermi-LAT diffuse $gamma$-ray data can be explained by simply enlarging the normalization of the electron spectrum without introduce any new sources, which may indicate that the current constraints on the dark matter models can be much stronger given a precise background estimate.

Discriminating different scenarios to account for the cosmic $e^pm$ excess by synchrotron and inverse Compton radiation

The excesses of the cosmic positron fraction recently measured by PAMELA and the electron spectra by ATIC, PPB-BETS, Fermi and H.E.S.S. indicate the existence of primary electron and positron sources. The possible explanations include dark matter annihilation, decay, and astrophysical origin, like pulsars. In this work we show that these three scenarios can all explain the experimental results of the cosmic $e^pm$ excess. However, it may be difficult to discriminate these different scenarios by the local measurements of electrons and positrons. We propose possible discriminations among these scenarios through the synchrotron and inverse Compton radiation of the primary electrons/positrons from the region close to the Galactic center. Taking typical configurations, we find the three scenarios predict quite different spectra and skymaps of the synchrotron and inverse Compton radiation, though there are relatively large uncertainties. The most prominent differences come from the energy band $10^4sim 10^9$ MHz for synchrotron emission and $gtrsim 10$ GeV for inverse Compton emission. It might be able to discriminate at least the annihilating dark matter scenario from the other two given the high precision synchrotron and diffuse $gamma$-ray skymaps in the future.