Detection of the positron annihilation gamma ray line from the galactic center region

We present the results of a cosmic gamma ray line search made with a high energy resolution detector. We have made a positive detection of the 511 keV positron annihilation line in the direction of the galactic center. We have analysed our data assuming either a point source or an extended source. We conclude, from comparison with the results of other authors, that the measurements are consistent with an extended source between -300 < l < +300. We present also upper limits for other theoretically predicted lines. (orig.)