Millisecond pulsars and the Galactic Center gamma-ray excess: the importance of luminosity function and secondary emission

International audienceSeveral groups of authors have analyzed Fermi LAT data in a region around theGalactic Center finding an unaccounted gamma-ray excess over diffusebackgrounds in the GeV energy range. It has been argued that it is difficult oreven impossible to explain this diffuse emission by the leading astrophysicalcandidates - millisecond pulsars (MSPs). Here we provide a new estimate of thecontribution to the excess by a population of yet unresolved MSP located in thebulge of the Milky Way. We simulate this population with the GALPLOT package byadopting a parametric approach, with the range of free parameters gauged on theMSP characteristics reported by the second pulsar catalogue (2PC). We find thatthe conclusions strongly depend on the details of the MSP luminosity function(in particular, its high luminosity end) and other explicit or tacitassumptions on the MSP statistical properties, which we discuss. Notably, forthe first time we study the importance of the possible secondary emission ofthe MSPs in the Galactic Center, {i.e. the emission via inverse Compton lossesof electrons injected in the interstellar medium. Differently from a majorityof other authors, we find that within current uncertainties a large if notdominant contribution of MSPs to the excess cannot be excluded. We also showthat the sensitivities of future instruments or possibly already of the latestLAT data analysis (Pass 8) provide good perspectives to test this scenario byresolving a significant number of MSPs