The imprint of Gould's Belt on the local cosmic-ray electron spectrum

Abstract

Recent analyses have shown that if the sources of cosmic-rays are discrete, as are supernova remnants, then the spectra of cosmic-ray electrons vary greatly with location and time and the locally measured electron spectrum may be not representative of the electron spectra elsewhere in the Galaxy. We have continued the earlier studies by investigating the impact of the star forming region Gould's Belt on the local electron spectrum at GeV to TeV energies. Our results indicate that if the electron sources in Gould's Belt are continous, the local electron spectrum would be slightly hardened with a spectral index increase of ∆s ≈ 0.07 due to the higher SN rate in the Belt. If the electron sources are discrete, which is the more probable case, the local electron spectrum above ∼30 GeV is variable with similar amplitude as without Gould's Belt. By the method of Monte Carlo, we have also studied the correlation of the local electron flux with that in nearby molecular cloud complexes. The high energy electron flux above 30 GeV near the Orion, Monoceros, Cassiopeia, Cepheus, and Perseus clouds does not vary in coordination with the local flux, but a correlation between the electron flux in the Taurus and Ophiuchus clouds and that in solar vicinity is indicated by our study, implying that the spatial correlation length is of the order of 200 pc at electron energies of 100 GeV and higher. This would permit hard γ-ray spectra from inverse Compton scattering to be produced in the more distant clouds, in agreement with the GeV excess observed towards Orion and Monoceros, without affecting the emissivity spectra of the very nearby clouds as in Taurus and Ophiuchus.