DIFFUSE γ-RAY EMISSION FROM GALACTIC PULSARS

Abstract

Millisecond Pulsars are second most abundant source population discovered by\nthe Fermi-LAT. They might contribute non-negligibly to the diffuse emission\nmeasured at high latitudes by Fermi-LAT, the IDGRB. Gamma-ray sources also\ncontribute to the anisotropy of the IDGRB measured on small scales by\nFermi-LAT. We aim to assess the contribution of the unresolved counterpart of\nthe detected MSPs population to the IDGRB and the maximal fraction of the\nmeasured anisotropy produced by this source class. We model the MSPs spatial\ndistribution in the Galaxy and the gamma-ray emission parameters by considering\nradio and gamma-ray observational constraints. By simulating a large number of\nMSPs populations, we compute the average diffuse emission and the anisotropy\n1-sigma upper limit. The emission from unresolved MSPs at 2 GeV, where the peak\nof the spectrum is located, is at most 0.9% of the measured IDGRB above 10\ndegrees in latitude. The 1-sigma upper limit on the angular power for\nunresolved MSP sources turns out to be about a factor of 60 smaller than\nFermi-LAT measurements above 30 degrees. Our results indicate that this\ngalactic source class represents a negligible contributor to the high-latitude\ngamma-ray sky and confirm that most of the intensity and geometrical properties\nof the measured diffuse emission are imputable to other extragalactic source\nclasses. Nevertheless, given the MSP distribution, we expect them to contribute\nsignificantly to the gamma-ray diffuse emission at low latitudes. Since, along\nthe galactic disk, the population of young Pulsars overcomes in number the one\nof MSPs, we compute the gamma-ray emission from the whole population of\nunresolved Pulsars in two low-latitude regions: the inner Galaxy and the\ngalactic center.\n