The Fermi-LAT GeV excess as a tracer of stellar mass in the Galactic bulge

Abstract

An anomalous emission component at energies of a few gigaelectronvolts and located towards the inner Galaxy is present in the Fermi-LAT data. At present, the two most promising explanations are the annihilation of dark matter particles or the presence of a large population of unresolved point sources, most probably millisecond pulsars, at the Galactic Centre. Here, we report an analysis of the excess characteristics using almost eight years of Pass 8 ULTRACLEAN Fermi-LAT data with SkyFACT—a tool that combines image reconstruction with template-fitting techniques. We find that an emission profile that traces stellar mass in the boxy and nuclear bulge is preferred over conventional dark matter profiles. A model including the bulge is favoured over a model with dark matter at 16σ.

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Fig. 1: Observed γ-ray flux in the inner Galaxy and GCE templates considered.
Fig. 2: Observed and modelled fluxes.
Fig. 3: Best-fit γ-ray spectra for each model component, as a function of photon energy, compared with the observed spectrum.
Fig. 4: Stellar mass versus observed γ-ray luminosity.

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Acknowledgements

We thank L. Athanassoula, D. Berge, G. Bertone, I. Cholis, R. Crocker, O. Macias, P. Serpico, T. Slatyer, A. Strong, J. Vink and G. Zaharijas for useful discussions. We acknowledge D. Gaggero for support provided with the DRAGON code. R.B. thanks the organizers and participants of the TeVPA 2017 mini workshop on the GCE for a fruitful discussion. Part of this work was carried out on the Dutch national e-infrastructure with the support of SURF Cooperative. This research is funded by NWO through the Vidi research programme ‘Probing the Genesis of Dark Matter’ (680-47-532; to E.S. and C.W.), and through a GRAPPA-PhD fellowship (022.004.017; to R.B.). F.C. acknowledges support from the Agence Nationale de la Recherche under the contract ANR-15-IDEX-02 (project ‘Unveiling the Galactic Centre Mystery’; GCEM (principal investigator: F.C.)).

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Bartels, R., Storm, E., Weniger, C. et al. The Fermi-LAT GeV excess as a tracer of stellar mass in the Galactic bulge. Nat Astron 2, 819–828 (2018). https://doi.org/10.1038/s41550-018-0531-z

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