Multi-Component Imaging of the Fermi Gamma-ray Sky in the Spatio-spectral Domain

Abstract

We perform two distinct spatio-spectral reconstructions of the gamma-ray sky in the range of 0.56-316 GeV based on Fermi Large Area Telescope (LAT) data. Both describe the sky brightness to be composed of a diffuse-emission and a point-source component. The first model requires minimal assumptions and provides a template-free reconstruction as a reference. It makes use of spatial and spectral correlations to distinguish between the different components. The second model is physics-informed and further differentiates between diffuse emission of hadronic and leptonic origin. For this, we assume parametric, but spatially varying energy spectra to distinguish between the processes and use thermal Galactic dust observations to indicate the preferred sites of hadronic interactions. To account for instrumental effects we model the point-spread, the energy dispersion, and the exposure of the telescope throughout the observation. The reconstruction problem is formulated as a Bayesian inference task, that is solved by variational inference. We show decompositions of the Gamma-ray flux into diffuse and point-like emissions, and of the diffuse emissions into multiple physically motivated components. The diffuse decomposition provides an unprecedented view of the Galactic leptonic diffuse emission. It shows the Fermi bubbles and their spectral variations in high fidelity and other areas exhibiting strong cosmic ray electron contents, such as a thick disk in the inner Galaxy and outflow regions. Furthermore, we report a hard spectrum gamma ray arc in the northern outer bubble co-spatial with the reported X-ray arc by the eROSITA collaboration. All our spatio-spectral sky reconstructions and their uncertainty quantification are publicly available.

Please see the journal version for a language-edited release of this manuscript (open-access): https://doi.org/10.1051/0004-6361/202243819

References in corpus (21)

• Giant Gamma-ray Bubbles from Fermi-LAT: AGN Activity or Bipolar Galactic Wind?
• Incremental Fermi Large Area Telescope Fourth Source Catalog
• The Spectrum of the Isotropic Diffuse Gamma-Ray Emission Derived From First-Year Fermi Large Area Telescope Data
• Background model systematics for the Fermi GeV excess
• The Spectrum and Morphology of the Fermi Bubbles
• Detection of large-scale X-ray bubbles in the Milky Way halo
• Gamma-ray sky points to radial gradients in cosmic-ray transport
• The Return of the Templates: Revisiting the Galactic Center Excess with Multi-Messenger Observations
• The diffuse $\gamma$-ray background is dominated by star-forming galaxies
• Gamma rays as probes of cosmic-ray propagation and interactions in galaxies
• 3D template-based $Fermi$-LAT constraints on the diffuse supernova axion-like particle background
• Geometric variational inference
• A neural simulation-based inference approach for characterizing the Galactic Center $\gamma$-ray excess
• Dissecting the inner Galaxy with $\gamma$-ray pixel count statistics
• Dim but not entirely dark: Extracting the Galactic Center Excess' source-count distribution with neural nets
• The contribution of Galactic TeV pulsar wind nebulae to Fermi-LAT diffuse emission
• A Phantom Menace: On the Morphology of the Galactic Center Excess
• Search for new cosmic-ray acceleration sites within the 4FGL catalog Galactic plane sources
• Mind the gap: The discrepancy between simulation and reality drives interpretations of the Galactic Center Excess
• Approximate Bayesian Computation Applied to the Diffuse Gamma-ray Sky
• Improved Modeling of the Discrete Component of the Galactic Interstellar Gamma-ray Emission and Implications for the Fermi-LAT Galactic Center Excess

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