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Context. Star-forming regions are gaining considerable interest in the high-energy astrophysics community as possible Galactic particle accelerators. In general, the role of electrons has not been fully considered in this kind of cosmic-ray source. However, the intense radiation fields inside these regions might make electrons significant gamma-ray contributors. Aims. We study the young and compact star-forming region NGC 3603, a well known gamma-ray emitter. Our intention is to test whether its gamma-ray emission can be produced by cosmic-ray electrons. Methods. We build a novel model by creating realistic 3D distributions of the gas and the radiation field in the region. We introduce these models into PICARD to perform cosmic-ray transport simulations and produce gamma-ray emission maps. The results are compared with a dedicated Fermi Large Area Telescope data analysis at high energies. We also explore the radio and neutrino emissions of the system. Results. We improve the existing upper limits of the NGC 3603 gamma-ray source extension. Although the gamma-ray spectrum is well reproduced with the injection of CR protons, it requires nearly 30\% acceleration efficiency. In addition, the resulting extension of the simulated hadronic source is in mild tension with the extension data upper limit. The radio data disfavours the lepton-only scenario. Finally, combining both populations, the results are consistent with all observables, although the exact contributions are ambiguous., Comment: 12 pages, 10 figures

The presence of delayed GeV emission after a strong transient, such as a GRB (Gamma-Ray Burst), in the VHE (Very-High Energy, $E>100$ GeV) band can be the signature of a non-zero magnetic field in the intergalactic medium. We used a synchrotron self-Compton multiwavelength model to infer an analytical description of the intrinsic VHE spectrum (corrected for absorption by the Extragalactic Background Light, EBL) of GRB$\,$190114C to predict the lightcurves and SEDs of the delayed emission with Monte Carlo simulations for different IGMF (Intergalactic Magnetic Field) configurations (strengths $B=8\times10^{-21}$ G, $10^{-20}$ G, $3\times 10^{-20}$G and correlation length $\lambda>1$ Mpc), and compared them with the Fermi-LAT (Fermi Large Area Telescope) limits computed for several exposure times. We found that Fermi LAT is not sensitive enough to constrain any IGMF strengths using GRB$\,$190114C., Comment: 8 pages, 3 figures, accepted for publication to Physical Review D

An incremental version of the fourth catalog of active galactic nuclei (AGNs) detected by the Fermi-Large Area Telescope is presented. This version (4LAC-DR3) derives from the third data release of the 4FGL catalog based on 12 years of E>50 MeV gamma-ray data, where the spectral parameters, spectral energy distributions (SEDs), yearly light curves, and associations have been updated for all sources. The new reported AGNs include 587 blazar candidates and four radio galaxies. We describe the properties of the new sample and outline changes affecting the previously published one. We also introduce two new parameters in this release, namely the peak energy of the SED high-energy component and the corresponding flux. These parameters allow an assessment of the Compton dominance, the ratio of the Inverse-Compton to the synchrotron peak luminosities, without relying on X-ray data., Comment: 13 pages, 7 figures, accepted for publication in The Astrophysical Journal Supplement Series. Fits files are available at https://fermi.gsfc.nasa.gov/ssc/data/access/lat/4LACDR3/ or alternatively at https://www.ssdc.asi.it/fermi4lac-DR3/table-4LAC-DR3-h.fits and https://www.ssdc.asi.it/fermi4lac-DR3/table-4LAC-DR3-l.fits

We present an incremental version (4FGL-DR3, for Data Release 3) of the fourth Fermi-LAT catalog of gamma-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 parameterization 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 yr intervals (not 2 month intervals). Among the 5064 original 4FGL sources, 16 were deleted, 112 are formally below the detection threshold over 12 yr (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., Comment: accepted in ApJS; follow-up paper to 1902.10045