Absorption dips in GRO J1655-40: mapping the inner accretion disk

Abstract

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 (~minute) and deep (down to ~8% of the out-of-dip intensity). Similar kind of dips were found in 90s measurements of the RXTE ASM during the same outburst. The occurrences of the dips are consistent with the optically determined orbital period, and were found between 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 dips. Using these results we are able constrain the extent of the absorbing medium and the central X-ray source. GRO J1655-40 was in the canonical high state during our PCA observations.