ROSAT AND OPTICAL OBSERVATIONS OF 2 X-RAY TRANSIENTS - MX-0836-42 ANDGS-0834-430

Two transient sources have been detected in hard X-rays by several ins truments at the end of 1990. We observed both sources with ROSAT in th e all sky survey and during the pointing phase. The positive detection of the sources in the ROSAT pointing observations made possible to de rive accurate positions for both sources. We also present optical imag es of the ROSAT error boxes obtained with the ESO NTT. Pulsations are clearly detected from GS 0834 - 430 with a period of 12.3203 +/- 0.001 5 s. The pulse profile is roughly sinusoidal with a 13% rms variation. The comparison with hard X-ray data and the possible nature of the so urces are discussed.