The Fermi Large Area Telescope (LAT) has detected hundreds of Galactic gamma-ray sources, most of them pulsars. But the Galaxy contains tens of thousands of such sources which are still undetected due to their low flux, or because of conflation of the foreground with sources. Characterizing the general properties of detected sources would allow us to estimate the contribution to the diffuse Galactic emission from these undetected sources, and in turn it would help detection of new sources and even searches for dark matter. We present updates on our long-term effort to characterize the general properties of Galactic gamma-ray sources with source population studies and to estimate the number of sources below the Fermi LAT flux sensitivity threshold.
Here we show results after adjusting a model of the detected and undetected pulsars for best fit parameters, by comparing it with the Fermi 4FGL-DR2 catalog. We identify preliminary best fit luminosity function slope, minimum luminosity, and source density for a given source distribution. We then use the model with the best fit parameters to determine the number of pulsars as a function of flux, including those below the sensitivity threshold.