1) Fermi-Lat had been in orbit for 4 years and will continue for another four years.
2) Seventy percent of photons are diffuse photons from our galaxy and majority of the rest thirty percent are diffuse photons from outside our galaxy.
3) The other detector onboard Fermi satellite is searching for gamma ray bursts.
4) Point sources for gamma ray that Fermi-LaT can detect include: Earth, Sun, pulsars and their relativistic wind nebula, AGN, galaxies, shock wave from SN remnants and etc