We report the discovery of emission features in the X-ray spectrum of GRO J1655-40 obtained with RXTE during the observation of 1997 , Feb 26 .
We have fitted the features firstly by two Gaussian lines which in four spectra analysed have average energies of 5.85 \pm 0.08 keV and 7.32 \pm 0.13 keV , strongly suggestive that these are the red and blue shifted wings of an iron disk line .
These energies imply a velocity of \sim 0.33 c. The blue wing is less bright than in the calculated profiles of disk lines near a black hole subject to Doppler boosting , however known Fe absorption lines in GRO J1655-40 at energies between \sim 7 and 8 keV can reduce the apparent brightness of the blue wing .
Secondly , we have fitted the spectra using the disk line model of Laor based on a full relativistic treatment plus an absorption line , and show that good fits are obtained .
This gives a restframe energy of the disk line between 6.4 and 6.8 keV indicating that the line is iron { K _ { \alpha } } emission probably of significantly ionized material .
The Laor model shows that the line originates in a region of the accretion disk extending from \sim 10 Schwarzschild radii from the black hole outwards .
The line is direct evidence for the black hole nature of the compact object and is the first discovery of a highly red and blue shifted iron disk line in a Galactic source .