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 50MeV to 1TeV, 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.
We present the results of a multi-frequency, time-averaged analysis of blazars included in the Candidate Gamma-ray Blazar Survey catalog. Our sample consists of 324 γ-ray detected (γ-ray loud) and 191 non γ-ray detected (γ-ray quiet) blazars, and we consider all the data up to 2016 April 1. We find that both the γ-ray loud and the γ-ray quiet blazar populations occupy similar regions in the WISE color-color diagram, and in the radio and X-ray bands γ-ray loud sources are brighter. A simple one-zone synchrotron inverse-Compton emission model is applied to derive the physical properties of both populations. We find that the central black hole mass and the accretion disk luminosity (L disk ) computed from the modeling of the optical-UV emission with a Shakura-Sunyaev disk reasonably matches with that estimated from the optical spectroscopic emission-line information. A significantly larger Doppler boosting in the γ-ray loud blazars is noted, and their jets are more radiatively efficient. On the other hand, the γ-ray quiet objects are more MeV-peaked, thus could be potential targets for next-generation MeV missions. Our results confirm the earlier findings about the accretion-jet connection in blazars; however, many of the γ-ray quiet blazars tend to deviate from the recent claim that the jet power exceeds L disk in blazars. A broadband study, considering a larger set of γ-ray quiet objects and also including BL Lacs, will be needed to confirm/reject this hypothesis and also to verify the evolution of the powerful high-redshift blazars into their low-power nearby counterparts.
We present the 2-100 keV spectral analysis of 30 candidate Compton-thick-(CT-)active galactic nuclei (AGNs) selected in the Swift-Burst Alert Telescope (BAT) 100 month survey. The average redshift of these objects is z 0.03 á ñ ~, and they all lie within ∼500 Mpc. We used the MyTorus model to perform X-ray spectral fittings both without and with the contribution of the Nuclear Spectroscopic Telescope Array (NuSTAR) data in the 3-50 keV energy range. When the NuSTAR data are added to the fit, 13 out of 30 of these objects (43% of the whole sample) have intrinsic absorption N H <10 24 cm −2 at the >3σ confidence level, i.e., they are reclassified from Compton thick to Compton thin. Consequently, we infer an overall observed fraction of the CT-AGN, with respect to the whole AGN population, lower than the one reported in previous works, as low as ∼4%. We find evidence that this overestimation of N H is likely due to the low quality of a subsample of spectra, either in the 2-10 keV band or in the Swift-BAT one.
The Hubble constant H 0 and matter density Ω m of the Universe are measured using the latest γray attenuation results from Fermi-LAT and Cherenkov telescopes. This methodology is based upon the fact that the extragalactic background light supplies opacity for very high energy photons via photon-photon interaction. The amount of γ-ray attenuation along the line of sight depends on the expansion rate and matter content of the Universe. This novel strategy results in a value of H 0 = 67.4 +6.0 −6.2 km s −1 Mpc −1 and Ω m = 0.14 +0.06 −0.07 . These estimates are independent and complementary to those based on the distance ladder, cosmic microwave background (CMB), clustering with weak lensing, and strong lensing data. We also produce a joint likelihood analysis of our results from γ rays and these from more mature methodologies, excluding the CMB, yielding a combined value of H 0 = 66.6 ± 1.6 km s −1 Mpc −1 and Ω m = 0.29 ± 0.02.
We present the analysis of a sample of 35 candidate Compton thick (CT-) active galactic nuclei (AGNs) selected in the nearby Universe (average redshift z ∼0.
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