Observations of high-energy gamma-rays with the Fermi Observatory

The Fermi Gamma-Ray Space Telescope is a satellite-based observatory that explores the gamma-ray sky in a wide energy range from a few keV to more than 300 GeV, allowing the investigation of many fields of gamma-ray astrophysics. Fermi will open a new and important window on a wide variety of phenomena, including black holes and active galactic nuclei, gamma-ray bursts, the origin of cosmic rays and supernova remnants and searches for hypothetical new phenomena such as supersymmetric dark matter annihilations. The primary instrument is the Large Area Telescope (LAT), which measures gamma-ray flux and spectra from 20 MeV to > 300 GeV and is a successor to the highly successful EGRET experiment on CGRO. The LAT has better angular resolution, greater effective area, wider field of view and broader energy coverage than any previous experiment in this energy range. The detectors were integrated with the spacecraft in December 2006 and Fermi has been launched on June, 11 2008 from Kennedy Space Flight Centre (NASA). In an early phase of the operations, a series of calibrations and performance measurements and monitoring were performed and the first sky images were collected. This paper will present a short review of the Fermi observatory physics and the first sky images collected during the first 6 months of the science phase of the mission

Solar gamma rays and modulation of cosmic rays in the inner heliosphere

The first evidence of the gamma-ray emission from the quiescent Sun was found in the archival EGRET data that was later confirmed by Fermi-LAT observations with high significance. This emission is produced by Galactic cosmic rays (CRs) penetrating the inner heliosphere and inter- acting with the solar atmosphere and optical photons. The solar emission is characterized by two spatially and spectrally distinct components: (i) disk emission due to the CR cascades in the solar atmosphere, and (ii) spatially extended inverse Compton (IC) emission due to the CR electrons scattering off of solar photons. The intensity of both components associated with Galactic CRs anti-correlate with the level of the solar activity being the brightest during solar minimum. In this paper we discuss updates of the models of the IC component of the emission based on CR measurements made at different levels of solar activity, and we make predictions for e- ASTROGAM and AMEGO, proposed low-energy gamma-ray missions.Comment: 7 pages, 3 figures, Proceedings of the 35th International Cosmic Ray Conference, ICRC201