DIFFUSE γ-RAY EMISSION FROM GALACTIC PULSARS

Millisecond Pulsars are second most abundant source population discovered bythe Fermi-LAT. They might contribute non-negligibly to the diffuse emissionmeasured at high latitudes by Fermi-LAT, the IDGRB. Gamma-ray sources alsocontribute to the anisotropy of the IDGRB measured on small scales byFermi-LAT. We aim to assess the contribution of the unresolved counterpart ofthe detected MSPs population to the IDGRB and the maximal fraction of themeasured anisotropy produced by this source class. We model the MSPs spatialdistribution in the Galaxy and the gamma-ray emission parameters by consideringradio and gamma-ray observational constraints. By simulating a large number ofMSPs populations, we compute the average diffuse emission and the anisotropy1-sigma upper limit. The emission from unresolved MSPs at 2 GeV, where the peakof the spectrum is located, is at most 0.9% of the measured IDGRB above 10degrees in latitude. The 1-sigma upper limit on the angular power forunresolved MSP sources turns out to be about a factor of 60 smaller thanFermi-LAT measurements above 30 degrees. Our results indicate that thisgalactic source class represents a negligible contributor to the high-latitudegamma-ray sky and confirm that most of the intensity and geometrical propertiesof the measured diffuse emission are imputable to other extragalactic sourceclasses. Nevertheless, given the MSP distribution, we expect them to contributesignificantly to the gamma-ray diffuse emission at low latitudes. Since, alongthe galactic disk, the population of young Pulsars overcomes in number the oneof MSPs, we compute the gamma-ray emission from the whole population ofunresolved Pulsars in two low-latitude regions: the inner Galaxy and thegalactic center.