Fermi Large Area Telescope Fourth Source Catalog

Abstract

We present the fourth Fermi Large Area Telescope catalog (4FGL) of γ-ray sources. Based on the first eight years of science data from the Fermi Gamma-ray Space Telescope mission in the energy range from 50MeV to 1TeV, it is the deepest yet in this energy range. Relative to the 3FGL catalog, the 4FGL catalog has twice as much exposure as well as a number of analysis improvements, including an updated model for the Galactic diffuse γ-ray emission, and two sets of light curves (one-year and two-month intervals). The 4FGL catalog includes 5064 sources above 4σ significance, for which we provide localization and spectral properties. Seventy-five sources are modeled explicitly as spatially extended, and overall, 358 sources are considered as identified based on angular extent, periodicity, or correlated variability observed at other wavelengths. For 1336 sources, we have not found plausible counterparts at other wavelengths. More than 3130 of the identified or associated sources are active galaxies of the blazar class, and 239 are pulsars.

Relativistic Jets in Gamma-Ray-Emitting Narrow-Line Seyfert 1 Galaxies

“…In the same way, the average photon index Γ γ of the γ-ray-emitting NLSy1 ranges between 2.2 and 2.9, a range of values usually observed in FSRQ [3,60]. For six of the nine sources the γ-ray spectrum is significantly curved (TS curv > 9 3 ), and a log-parabola model is preferred over a simple power-law model. In that case the spectral slope (α) and curvature parameter (β) have been reported in Table 1, together with the photon index obtained with the power-law model.…”

“…Observations with the Fermi Gamma-ray Space Telescope have revealed NLSy1 as a possible new class of γ-ray-emitting AGN with blazar-like properties [8]. It is a small class, consisting of only 9 bona-fide NLSy1 to date [3]. The continuous all-sky survey in γ-rays by Fermi-LAT will allow us to identify new γ-ray-emitting NLSy1 and to better characterize already known γ-ray sources belonging to this intriguing class of objects.…”

“…The γ-ray flaring activity of SBS 0846+513 and PMN J0948+0022 has been associated with a moderate spectral evolution, a behaviour observed also in bright FSRQ and low-synchrotron-peaked BL Lacs (e.g., [68]). 3 TS curv = 2 log(Likelihood(log-parabola)/Likelihood(power-law)), i.e., a comparison of the likelihood function changing only the spectral representation of the source. In addition to the nine NLSy1 reported in the 4FGL catalog, the γ-ray detection of other NLSy1 has been claimed in literature: FBQS J1102+2239 [64], FBQS J0956+2515 [69], NVSS J142106+385522 [59], and SDSS J164100.10+345452.7 [70].…”

“…Before the launch of the Fermi Gamma-ray Space Telescope satellite only two classes of AGN were known to generate strong relativistic jets, therefore to emit up to the γ-ray energy range: blazars and radio galaxies [1], both hosted in giant elliptical galaxies [2]. The observations by the Large Area Telescope (LAT) on board the Fermi satellite confirmed that the extragalactic γ-ray sky is dominated by blazars, with only a few radio galaxies detected [3,4]. However, the discovery by Fermi-LAT of variable γ-ray emission from a few radio-loud narrow-line Seyfert 1 galaxies (NLSy1) revealed the presence of a possible third class of AGN with powerful relativistic jets 1 (e.g., [6][7][8]).…”

A two-sided but significantly beamed jet in the supercritical accretion quasar IRAS F11119+3257

“…As the lower limit of the jet speed is higher than that observed in the powerful X-ray outflows (Tombesi et al 2015) and only a maximum jet speed of upto 0.5c is achievable for a radiative jet in a supercritical accretion disc (Sadowski & Narayan 2015), the jet components in IRAS F11119+3257 may not be driven by radiation pressure alone. These jet components are not subject to highly relativistic beaming since they have an extended morphology, relatively low T B , and no high-energy γ-ray counterpart in the Fermi LAT 8-Year Point Source Catalog (Abdollahi et al 2020).…”