THE DISTANCE OF THE SOFT GAMMA-REPEATER SGR-1806-20

We present (CO)-C-12 (J = 1-0) observations in the direction of the so ft gamma repeater SGR 1806-20 with the SEST telescope. We detected sev eral molecular clouds, and we discuss in this paper the implications o f these observations for the distance to the X-ray counterpart AX 1805 .7-2025, the supernova remnant G10.0-0.3 and the very luminous O9-B2 s tar detected in the line of sight. The distance of SGR 1806-20 is esti mated to be 14.5+/-1.4 kpc and this soft gamma repeater is very likely associated with one of the brightest H II regions in the Galaxy, W31. The large size of G10.0-0.3 (25 x 38 pc) for a young supernova remnan t possibly powered by a central pulsar (AX 1805.7-2025) indicates that G10.0-0.3 could be expanding in the very low density region produced by the wind of the blue star.