ABSORPTION DIPS IN GRO J1655-40 - MAPPING THE INNER ACCRETION DISK

Using the RXTE PCA we discovered dips in the X-ray light curves of the black-hole candidate GRO J1655-40 during outburst. They are short (si milar to minute) and deep (down to similar to 8% Of the out-of-dip int ensity). Similar kind of dips were found in 90 s measurements of the R XTE ASM: during the same outburst. The occurrences of the dips are con sistent with the optically determined orbital period. and were found b etween photometric orbital phases 0.72 and 0.86. This constitutes the first evidence for orbital variations in X-rays for GRO J1655-40. The PCA data indicate that an absorbing medium is responsible for these di ps. Using these results we are able constrain the extent of the absorb ing medium and the central X-ray source. GRO J1655-40 was in the canon ical high state during our PCA observations.