Microquasars are accreting black holes or neutron stars in binary systems with associated relativistic jets. Despite their frequent outburst activity, they have never been unambiguously detected emitting high-energy gamma rays. The Fermi Large Area Telescope (LAT) has detected a variable high-energy source coinciding with the position of the x-ray binary and microquasar Cygnus X-3. Its identification with Cygnus X-3 is secured by the detection of its orbital period in gamma rays, as well as the correlation of the LAT flux with radio emission from the relativistic jets of Cygnus X-3. The gamma-ray emission probably originates from within the binary system, opening new areas in which to study the formation of relativistic jets
Cosmic-ray background fluxes were modeled on the basis of existing measurements and theories and are presented here. The model, originally developed for the Gamma-Ray Large Area Space Telescope (GLAST ) balloon experiment, covers the entire solid angle (4 sr), the sensitive energy range of the instrument ($10 MeV to 100 GeV ), and the abundant components (proton, alpha particle, e À , e þ , À , þ , and gamma ray). It is expressed in analytic functions in which modulations due to solar activity and the Earth's geomagnetism are parameterized. Although the model is intended to be used primarily for the GLAST balloon experiment, model functions in low Earth orbit are also presented and can be used for other high-energy astrophysical missions. The model has been validated via comparison with the data of the GLAST balloon experiment.
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