Gamma Rays from Interstellar Medium

The study of galactic diffuse gamma emission will be one of the main scientific objectives of AGILE, the ASI satellite for gamma-ray astronomy that will be launched in 2006. It will be able to cover 3 sr of sky with one single pointing with an effective area about one half of that of EGRET. This means that AGILE will collect, for the same observing time, a number of diffuse photons larger by a factor of two. AGILE will also be the gamma-ray imager with the better angular resolution of ever. In order to better exploit these capabilities, a very accurate model of the Galactic diffuse emission is required for the analysis of AGILE data.

The gamma emissivity is supposed, as in the EGRET model, to be produced by the interaction of cosmic rays with the interstellar medium through three physical process: proton-proton collision, bremsstrahlung and inverse compton. Therefore, to build a gamma ray emmissivity map of the galaxy it is necessary to know the 3D distributions of cosmic rays and of cosmic-ray targets, namely interstellar matter, given mainly by atomic hydrogen and molecular clouds, and interstellar radiation field.

• Contents
• Introduction
• Gamma-Ray Emissivity of the Interstellar Medium
  • The Interstellar Matter
    • The Molecular Clouds
      • The 2.6 mm line
    • The Atomic Hydrogen
      • The 21 cm line
    • The Ionized Hydrogen
  • The Interstellar Radiation Field
  • The magnetic field
  • Cosmic Rays
    • Cosmic Electrons
    • Cosmic Protons
  • The physical processes producing gamma-ray emissivity
    • Proton-Proton collisions
      • The cross section
    • Electron Bremsstrahlung
    • Inverse Compton
  
  
• Modeling the Gamma-Ray Emission of the Galaxy
  • The EGRET observations and the EGRET diffuse emission model
  • Beyond the EGRET model
  • The AGILE diffuse gamma-ray emission model
  • Mapping the matter distribution in the Galaxy
  • Line broadening and anomalous velocities
  • The dynamical ambiguity
  • Rotation curve
  • Diffuse matter distribution
  • Interstellar Radiation Field
  • Cosmic Rays
  
  
• Observing the Diffuse Emission
  • The gamma-ray sky
  • New vs old model
  • Model vs Observations
  • AGILE and the Diffuse -ray emission
  • A simulated AGILE observation
  
  
• AGILE performances optimization
  • The AGILE instrument
  • On-board tracks reconstruction
    • Event reconstruction in pair production detectors
    • The ''Kalmaex Algorithm''
    • Simulation Results
    • Background rejection
  • On-ground tracks reconstruction
    • Spectral capabilities
  
  
• Bibliography
• About this document ...