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

Juan Zhang, Xiao-jun Bi, Jia Liu, Si-Ming Liu, Peng-fei Yin, Qiang Yuan, Shou-hua Zhu

TL;DR

This paper investigates whether Galactic-center photon emissions can distinguish among three explanations for the cosmic $e^\

Abstract

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 $10^4\sim 10^9$ 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 $γ$-ray skymaps in the future.

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

TL;DR

This paper investigates whether Galactic-center photon emissions can distinguish among three explanations for the cosmic $e^\

Abstract

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 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 MHz for synchrotron emission and 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 -ray skymaps in the future.

Paper Structure

This paper contains 12 sections, 11 equations, 11 figures.

Table of Contents

  1. Introduction
  2. Different scenarios to account for the $e^\pm$ data
  3. Synchrotron radiation from the three scenarios
  4. Results from the three scenarios
  5. The WMAP haze
  6. Diffuse $\gamma$-rays from IC scattering
  7. Discussion on the uncertainties of prediction
  8. Particle physics model of DM
  9. Spatial distribution of DM
  10. Propagation model
  11. Other astrophysical uncertainties
  12. Summary and conclusion

Figures (11)

  • Figure 1: Left: The positron fractions predicted by the three scenarios after solar modulation, compared with HEAT Barwick:1997igCoutu:2001jy and PAMELA Adriani:2008zr data. Right: The total electron+positron fluxes of the three scenarios, compared with observations of ATIC Chang:2008zz, PPB-BETS Torii:2008xu, H.E.S.S. Collaboration:2008aaAharonian:2009ah and Fermi Collaboration:2009zk. We assume DM annihilates or decays into pure lepton final states with equal branching ratios to $e^+e^-$, $\mu^+\mu^-$ and $\tau^+\tau^-$.
  • Figure 2: The average synchrotron spectra of the three scenarios within a bin size of $20^\circ\times20^\circ$ around GC and anti-GC, respectively.
  • Figure 3: The synchrotron latitude profile for $|l|<10^\circ$ (left) and longitude profile for $|b|<10^\circ$ (right), at the frequency of 61 GHz. The solid black line indicates the contribution from background electrons and positrons, and the other lines represent the total synchrotron intensities from the three scenarios together with the background respectively.
  • Figure 4: Residual synchrotron intensities after subtracting the background for the three scenarios, compared with WMAP Haze data Dobler:2007wv at five different frequencies.
  • Figure 5: The contributions to the diffuse $\gamma$-ray spectra in the inner Galaxy of the three scenarios for two sky regions, compared with the EGRET data Hunter:1997we.
  • ...and 6 more figures