3.1 COMPTON GAMMA RAY OBSERVATORY

The Compton Gamma Ray Observatory (CGRO) was launched in April 1991 with a broad range of science objectives including the understanding of gamma-ray bursts, studies of black holes and neutron stars, the search for sites of nucleosynthesis, probing the galaxy through the interaction of cosmic rays with the interstellar medium, and studying the nature of active galaxies in gamma rays. While significant insight has already emerged in these areas, unanticipated discoveries have challenged our understanding of the conditions and energy-generating mechanisms for many astronomical sources, as indicated in sections 1 and 2.

Figure 3.1 - The Compton Gamma Ray Observatory during it's deployment.

CGRO continues to operate flawlessly and none of the instruments, except EGRET, has life-limiting consumables. Over 700 scientists from 23 countries have participated in the CGRO Guest Investigator program. One additional orbit reboost is expected to provide an operational capability for the Observatory well into the next century. EGRET has a limited supply of spark chamber gas which is being conserved through carefully selected observations and operating modes. Through this conservation program, EGRET expects to support a few limited science observations and targets of opportunity over the next five years. The science contributions which are anticipated from future CGRO observations are:

• Solving the GRB mystery. Counterparts may be identified using the near real-time BATSE and COMPTEL notification system and the BACODINE-triggered ground observer network.

• Continued all-sky monitoring for transients, X-ray pulsars, and sources of e+e- annihilation radiation.

• Nucleosynthesis in Type Ia supernova. OSSE and COMPTEL have the sensitivity to study gamma-ray lines from such supernovae to nearly 10 Mpc.

• Continued galactic plane observations with OSSE and COMPTEL to improve the sensitivity to diffuse line emissions such as ⁶⁰Fe and ⁴⁴Ti .

• High energy emission during the next solar maximum. CGRO may well provide the only opportunity to observe the Sun in gamma rays during the entire next solar maximum.

• Continued multiwavelength observations of AGNs.

• Testing nucleosynthesis models for novae; ²²Na emission from novae within 1-2 kpc may be detectable.