Gamma-Ray Observatory

Astronomy s new eyes carry code names like HST (Hubble Space Telescope), XMM (X-ray Multi-Mirror) and GRO (Gamma-Ray Observatory). Each wavelength region has its own squadron, extended by future spacecraft that take us ever further towards sensitivity and detailed analysis of images and spectra. 

UV, X-ray and gamma-ray observatories are all space-borne because these wavelengths are blocked by the Earth s atmosphere. And what could be more natural than to place eyes in orbits But who sent them up there and why Astrophysicists are no longer naive when it comes to the relationship between the tools of military surveillance and those of astronomy. And this is not a recent invention. Galileo himself offered his refracting telescope to the delighted dignitaries of the Venetian senate in order to draw attention to its military potential. His salary was immediately doubled and he was appointed professor at the University of Padua ... 

Fig. 4.4. All-sky map in the light of the 1.809 MeV gamma-ray hne from radioactive aluminium-26. The galactic distribution of aluminium-26, based on data from the COMPTEL (Compton Telescope) experiment aboard the GRO (Gamma-Ray Observatory), suggests that this isotope is dispersed across the Galaxy by the most massive stars, Wolf-Rayet stars and supernovas. Al is formed by the reaction Mg -b p — A1 -b y. This radioactive isotope has a lifetime of about million years and is ejected into space before it begins to decay.

The search for titanium-44 was undertaken by the gamma spectrometer aboard the Gamma-Ray Observatory (GRO). The 1.15 MeV line was detected in the direction of Cassiopeia A and Vela, two recent supernova remnants. Mapping the Galaxy in the 1.15 MeV line will undoubtedly be one of the main objectives of the European satellite INTEGRAL, a unique space-borne experiment in which Erance is deeply involved. ... 

RECENT RESULTS FROM THE MILAGRO GAMMA RAY OBSERVATORY... 

Milagro is a unique TeV gamma-ray observatory capable of continuously monitoring the overhead sky. The directions of gamma-rays impacting the earth s atmosphere are reconstructed through the detection of air-shower particles that reach the earth. The shower particles are detected with a 60m x 80m... 

Recent Results from the Milagro Gamma Ray Observatory... 

The Compton Telescope (COMPTEL) on the Compton Gamma Ray Observatory (CGRO) was the first instrument built to detect 7-rays and solar neutrons in space [Ryan et al., 1993a], COMPTEL observations of the June 15, 1991, solar neutron event were the first that allowed to generate an image of the Sun in neutrons [Ryan et al., 1993b Nieminen, 1997],... 

With COMPTEL on the Gamma-ray Observatory, the concept has definitely proven its unique potential for MeV gamma-ray astronomy (Schonfelder et al. 1993). 

One method in which this division is explicit is maximum entropy (Max-Ent) which has proved to be very effective in producing images from the COMPTEL instrument on the Compton Gamma Ray Observatory CGRO. In this paper I briefly describe MaxEnt and illustrate applications to COMPTEL data for imaging of continuum emission from point sources and for imaging the full sky. Applications to line emission are covered by R. Diehl in an accompanying paper. I also mention some new developments in Bayesian methods. 

The galactic 1.806 MeV emission from COMPTEL on the Compton Gamma Ray Observatory has mapped the distribution of Al within the galactic plane. Although it is possible that the A1 is from a number of point sources it seems more likely that the emission is extended, and has structure on scales of < 4 . 

---