Incremental Fermi Large Area Telescope Fourth Source Catalog

Abstract

We present an incremental version (4FGL-DR3, for Data Release 3) of the fourth Fermi -LAT catalog of γ-ray sources. Based on the first twelve years of science data in the energy range from 50 MeV to 1 TeV, it contains 6658 sources. The analysis improves on that used for the 4FGL catalog over eight years of data: more sources are fit with curved spectra, we introduce a more robust spectral parametrization for pulsars, and we extend the spectral points to 1 TeV. The spectral parameters, spectral energy distributions and associations are updated for all sources. Light curves are rebuilt for all sources with 1-year intervals (not 2-month intervals).Among the 5064 original 4FGL sources, 16 were deleted, 112 are formally below the detection threshold over 12 years (but are kept in the list), while 74 are newly associated, 10 have an improved association and seven associations were withdrawn. Pulsars are split explicitly between young and millisecond pulsars. Pulsars and binaries newly detected in LAT sources, as well as more than 100 newly classified blazars, are reported. We add three extended sources and 1607 new point sources, mostly just above the detection threshold, among which eight are considered identified and 699 have a plausible counterpart at other wavelengths.We discuss degree-scale residuals to the global sky model and clusters of soft unassociated point sources close to the Galactic plane, which are possibly related to limitations of the interstellar emission model and missing extended sources.

Fermi LAT Gamma-ray Detection of the Recurrent Nova RS Ophiuchi during its 2021 Outburst

“…With a peak flux, F γ (>0.1 GeV) 6 × 10 −6 ph cm −2 s −1 , the RS Oph 2021 outburst is the brightest nova detected thus far in γ rays by the LAT. The previous brightest LAT-detected nova was the classical nova V906 Car 2018 with a peak F γ (>0.1 GeV) 4 × 10 −6 ph cm −2 s −1 (Jean et al 2018;Aydi et al 2020), although its early γ rays were missed due to an anomaly with a Fermi solar panel assembly motor (Abdollahi et al 2022). The detection of > 5 GeV and up to ∼20-23 GeV energy photons ( § 2.3) help constrain the high-energy portion of the SEDs in our modeling of select intervals.…”

“…We constructed a spatial and spectral model of our ROI starting from the 4FGL catalog incremental data release 3 (DR3; Abdollahi et al 2020Abdollahi et al , 2022 based on twelve years of LAT data. We included all DR3 sources within 35 • of the ROI center as well as a model for the Galactic diffuse emission (gll iem v07.fits) and a diffuse isotropic emission Figure 1.…”

The Isotropic γ-ray Emission above 100 GeV: Where Do Very High-energy γ-rays Come From?

“…For energies > 100 GeV and Galactic latitudes b > |50 • |, we would expect the extragalactic isotropic γ-ray emission to be dominated by blazars or other potential VHE sources, like star-forming and radio galaxies. It is unreasonable to assume that these VHE equivalent photons originate from Galactic VHE objects, like pulsar wind nebulae and supernova remnants, as out of 62 such objects listed in 4FGL-DR3, only two have b ∼ 32 • (both in the Large Magellanic Cloud), and the rest has b < |10 • | (Abdollahi et al 2020(Abdollahi et al , 2022. Above |50 • | in Galactic latitude, the majority of VHE γ-ray emitters must be extragalactic.…”

Investigating the correlations between IceCube high-energy neutrinos and Fermi-LAT gamma-ray observations

“…The 3FHL is constructed based on 7 years of Fermi-LAT data in the 10 GeV-2 TeV energy range [76]. Besides the 3FHL, other samples considered in this work include, the gamma-ray sources of the fourth Fermi-LAT catalog (4FGL-DR3, for Data Release 3) [77,78] and the fourth catalog of active galatic nuclei (4LAC-DR2, for Data Release 2) [79,80]. All these samples are summarized in Table I.…”

“…The majority of the unassociated sources at high latitudes are also AGN origins. Here we adopt the latest 4FGL-DR3 [77,78] and 4LAC-DR2 [79,80] catalogs, as 3. Like the above 3FHL and HEE searches, the distribution is consistent with Gaussian fluctuations, with no sign of statistically significant neutrino emission.…”