The Fermi-LAT long-term transient sources (1FLT)

All sources detected with a statistical significance above 4{sigma} in at least one monthly bin were listed in the final catalog. The 1FLT catalog contains 142 transient {gamma}-ray sources that are not included in the 4FGL-DR2 catalog. Many of these sources (102) have been confidently associated with active galactic nuclei (AGNs): 24 are associated with flat-spectrum radio quasars, 1 with a BL Lac object, 70 with blazars of uncertain type, 3 with radio galaxies, 1 with a compact steep-spectrum radio source, 1 with a steep-spectrum radio quasar, and 2 with AGNs of other types.

The remaining 40 sources have no candidate counterparts at other wavelengths. The median {gamma}-ray spectral index of the 1FLT-AGN sources is softer than that reported in the latest Fermi-LAT AGN general catalog. This result is consistent with the hypothesis that detection of the softest {gamma}-ray emitters is less efficient when the data are integrated over year-long intervals.