The Fourth Catalog of Active Galactic Nuclei Detected by the Fermi Large Area Telescope

Ajello, M.; Angioni, R.; Axelsson, M.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Becerra Gonzalez, J.; Bellazzini, R.; Bissaldi, E.; Bloom, E. D.; Bonino, R.; Bottacini, E.; Bruel, P.; Buson, S.; Cafardo, F.; Cameron, R. A.; Cavazzuti, E.; Chen, S.; Cheung, C. C.; Ciprini, S.; Costantin, D.; Cutini, S.; D'Ammando, F.; de la Torre Luque, P.; de Menezes, R.; de Palma, F.; Desai, A.; Di Lalla, N.; Di Venere, L.; Domínguez, A.; Dirirsa, F. Fana; Ferrara, E. C.; Finke, J.; Franckowiak, A.; Fukazawa, Y.; Funk, S.; Fusco, P.; Gargano, F.; Garrappa, S.; Gasparrini, D.; Giglietto, N.; Giordano, F.; Giroletti, M.; Green, D.; Grenier, I. A.; Guiriec, S.; Harita, S.; Hays, E.; Horan, D.; Itoh, R.; Jóhannesson, G.; Kovac'Evic', M.; Krauss, F.; Kreter, M.; Kuss, M.; Larsson, S.; Leto, C.; Li, J.; Liodakis, I.; Longo, F.; Loparco, F.; Lott, B.; Lovellette, M. N.; Lubrano, P.; Madejski, G. M.; Maldera, S.; Manfreda, A.; Martí-Devesa, G.; Massaro, F.; Mazziotta, M. N.; Mereu, I.; Meyer, M.; Migliori, G.; Mirabal, N.; Mizuno, T.; Monzani, M. E.; Morselli, A.; Moskalenko, I. V.; Negro, M.; Nemmen, R.; Nuss, E.; Ojha, L. S.; Ojha, R.; Omodei, N.; Orienti, M.; Orlando, E.; Ormes, J. F.; Paliya, V. S.; Pei, Z.; Peña-Herazo, H.; Persic, M.; Pesce-Rollins, M.; Petrov, L.; Piron, F.; Poon, H.; Principe, G.; Rainò, S.; Rando, R.; Rani, B.; Razzano, M.; Razzaque, S.; Reimer, A.; Reimer, O.; Schinzel, F. K.; Serini, D.; Sgrò, C.; Siskind, E. J.; Spandre, G.; Spinelli, P.; Suson, D. J.; Tachibana, Y.; Thompson, D. J.; Torres, D. F.; Torresi, E.; Troja, E.; Valverde, J.; van Zyl, P.; Yassine, M.

doi:10.3847/1538-4357/ab791e

The fourth catalog of active galactic nuclei (AGNs) detected by the Fermi Gamma-ray Space Telescope Large Area Telescope (4LAC) between 2008 August 4 and 2016 August 2 contains . It includes 85% more sources than the previous 3LAC catalog based on 4 yr of data. AGNs represent at least 79% of the high-latitude sources in the fourth Fermi-Large Area Telescope Source Catalog (4FGL), which covers the energy range from 50 MeV to 1 TeV. In addition, gamma-ray AGNs are found at low Galactic latitudes. Most of the 4LAC AGNs are blazars (98%), while the remainder are other types of AGNs. The blazar population consists of 24% Flat Spectrum Radio Quasars (FSRQs), 38% BL Lac-type objects, and 38% blazar candidates of unknown types (BCUs). On average, FSRQs display softer spectra and stronger variability in the gamma-ray band than BL Lacs do, confirming previous findings. All AGNs detected by ground-based atmospheric Cerenkov telescopes are also found in the 4LAC.