Turmoil on the accretion disk of GRO J1655-40

During the 1996/1997 outburst of the X-ray transient GRO J1655-40 the Wide Field Cameras onboard BeppoSAX observed the system with nearly continuous coverage during some stages of this outburst. On two occasions we find clear evidence for frequent dipping behaviour, characterized by several absorption dips occurring within one binary orbit. However, during preceding and following binary orbits there is no sign of such dips at the same range of orbital phases. We also collected light curves of absorption dips as seen with other X-ray instruments. Although the 65 dips that were collected occur preferably between orbital phases 0.68 and 0.92, there is evidence that the morphology of the material causing the dips is changing over just one binary orbit. The short duration (~minutes) and phasing of the dips are discussed in the framework of models where the stream from the companion star encounters a hot outer rim on the accretion disk.