Gamma-ray Line Astronomy *

Gamma-ray lines from radioactive isotopes, ejected into interstellar space by cosmic nucleosynthesis events, are observed with new space telescopes. The Compton Observatory had provided a sky survey for the isotopes 26 Al, detecting supernova radioactivity and the diffuse glow of long-lived radioactivity from massive stars in the Galaxy. High-resolution spectroscopy is now being exploited with Ge detectors: Since 2002, with ESA's INTEGRAL satellite and the RHESSI solar imager two space-based Ge-gamma-ray telescopes are in operation, measuring Doppler broadenings and line shape details of cosmic gamma-ray lines. First year's results include a detection and line shape measurement of annihilation emission, and 26 Al emission from the inner Galaxy and from the Cygnus region. 60 Fe gamma-ray intensity is surprisingly low; it may have been detected by RHESSI at 10% of the 26 Al brightness, yet is not seen by INTEGRAL. 44 Ti emission from Cas A and SN1987A is being studied; no other candidate young supernova remnants have been found through 44 Ti. 22 Na from novae still is not seen.