Out of the 5066 4FGL sources, 3131 are blazars: 1116 BL Lacs, 686 FSRQs, and 1329 blazar candidates of uncertain type (BCUs). LAT 8-year Source Catalog (4FGL) The Large Area Telescope (LAT) on board NASA's Fermi Gamma-ray Space Telescope (launched June 11, 2008) surveys the entire sky each day.
We perform a Binned likelihood analysis and a Bayesian analysis of the Crab, optimizing the parameters of the Crab Pulsar (PSR J0534+2200) keeping fixed the parameters of the Crab Nebula.
The optional "e", "i" and
"s" designators are explained in the caveats below. The latest Fermi-LAT catalogue is the LAT 8-yr Source Catalogue 4FGL (The Fermi-LAT collaboration 2019a), which lists 5066 γ-ray sources, about 2000 more than the previous 3FGL catalogue (Acero et al. It must be noted that the level of spectral distortion due to energy dispersion depends also on the source spectrum, especially in the case of sharp features (like an exponential cutoff). LAT 4-year Source Catalog (3FGL) The Large Area Telescope (LAT) on board NASA's Fermi Gamma-ray Space Telescope (launched June 11, 2008) observes in the 20 MeV to 300 GeV energy range.
For analysis using older diffuse models (gll_iem_v06.fits or older) the energy dispersion should also be turned off for the diffuse model, as well as any point-like or extended sources for which the spectral parameters are fixed to the 3FGL (also applies to 2FGL and 1FGL) values. In the model, the nebula is described by two sources, one representing the synchrotron spectrum, the othet the Inverse Compton emission. The effect of energy dispersion is relevant at energies < 300 MeV, but also induces a smaller systematic offset in the flux normalization at higher energies. The finite energy resolution of the LAT called the energy dispersion has been characterized by the LAT team and this information is part of the
For Pass 8, the energy resolution is <10% between 1 GeV and 100 GeV, which is sufficient to limit the spectral distortion to less than 5% in this energy range.
© Copyright 2017--2020, G.Vianello, J. M. Burgess, N. Di Lalla, N. Omodei For
analysis using older diffuse models (gll_iem_v06.fits or older) the
energy dispersion should also be turned off for the diffuse model, as
well as any point-like or extended sources for which the spectral
parameters are fixed to the 3FGL (also applies to 2FGL and 1FGL) values.
The LAT 8-year Source Catalog is currently available as a FITS
file to be used for data analysis within the
Fermitools. The Fermi LAT collaboration has released, at the end of February 2019, an early version of the fourth FermiGamma-ray LAT (4FGL) source catalog, based on the first eight years of LAT science data collection. free and fix parameters of the sources in the model, and how to perform a spectral analysis using the fermipy plugin.Letâs interrogate the 4FGL to get the sources in a radius of 20.0 deg around the CrabThis gets a 3ML model (a Model instance) from the table above, where every source in the 4FGL becomes a Source instance.