Abstract
We report the detection of high-energy gamma rays from the quiescent Sun with the Large Area Telescope (LAT) on board the Fermi Gamma-Ray Space Telescope (Fermi) during the first 18 months of the mission. These observations correspond to the recent period of low solar activity when the emission induced by cosmic rays is brightest. For the first time, the high statistical significance of the observations allows clear separation of the two components: the point-like emission from the solar disk due to cosmic ray cascades in the solar atmosphere, and extended emission from the inverse Compton scattering of cosmic ray electrons on solar photons in the heliosphere. The observed integral flux (>100 MeV) from the solar disk is (4.6 +/- 0.2 [statistical error] +1.0/-0.8 [systematic error]) x10^{-7} cm^{-2} s^{-1}, which is ~7 times higher than predicted by the "nominal" model of Seckel et al. (1991). In contrast, the observed integral flux (>100 MeV) of the extended emission from a region of 20 deg radius centered on the Sun, but excluding the disk itself, (6.8 +/-0.7 [stat.] +0.5/-0.4 [syst.]) x10^{-7} cm^{-2} s^{-1}, along with the observed spectrum and the angular profile, are in good agreement with the theoretical predictions for the inverse Compton emission.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.