Speaker
Description
The gamma radiation produced in cosmic-ray and gas interactions has been used to probe the cosmic-ray spectrum in several clouds to distances of a few hundred parsecs around the Sun. Early measurements made with Fermi LAT data were found in good agreement with the proton and alpha cosmic-ray spectra measured in the Solar System, given the 10-15% uncertainty in target gas mass that is inherent to HI line observations (Casandjian 2015, Grenier et al. 2015). The local cosmic-ray uniformity was later questioned (Orlando 2018), then challenged by the finding of a 34% loss of cosmic rays in the nearby Eridu cirrus (Joubaud et al. 2020).
We have revisited the gamma-ray emissivity spectrum one would expect per gas nucleon from hadronic and bremsstrahlung emission using the latest cosmic-ray spectra inferred at the Sun (outside the heliosphere) from the existing data on different nuclear species and leptons. We have also used improved cross sections for photon production in nucleus-nucleus interactions.
We will discuss how the local variations in cosmic-ray flux, of order $\pm$30%, relate in 3D to the contrasted gas distribution and gross magnetic-field configuration of the local interstellar valley.
Keywords
cosmic rays, gamma rays, local interstellar medium, propagation
| Subcategory | Experimental Results |
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