Echoes from an Irradiated Disc in GRO J1655-40
  We demonstrate correlated rapid variability between the optical/UV and X-ray emission for the first time in a soft X-ray transient, GRO J1655-40: HST light curves show similar features to those seen by RXTE, but with mean delay of 10-20s. We interpret the correlations as due to reprocessing of X-rays into optical and UV emission, with a delay due to finite light travel time, and thus perform echo mapping of the system. The time-delay distribution has a mean of 14.6s +/- 1.4 and dispersion (i.e. the standard deviation of the distribution) of 10.5s +/- 1.9 at binary phase 0.4. Hence we identify the reprocessing region as the accretion disc rather than the mass donor star. 
R. I. Hynes (U. Sussex), K. O'Brien, Keith Horne (U. St. Andrews), W.   Chen (U. Maryland, NASA/GSFC), C. A. Haswell (U. Sus...