  The discovery is reported of emission features in the X-ray spectrum of GRO
J1655-40 obtained using Rossi-XTE on 1997, Feb 26. The features have been
fitted firstly by two Gaussian lines, which in four spectra have average
energies of 5.85+/-0.08 keV and 7.32+/-0.13 keV, strongly suggestive that these
are the red- and blueshifted wings of an iron disc line from material with
velocity ~0.33 c. The blue wing is apparently less bright than expected for a
disc line subject to Doppler boosting, however, known absorption in the
spectrum of GRO J1655-40 at energies between ~7 and 8 keV can reduce the
apparent brightness of the blue wing. The spectra have also been fitted well
using the full relativistic disc line model of Laor, plus an absorption line.
This gives a restframe energy between 6.4 and 6.8 keV indicating that the line
is from highly ionized iron K_alpha. The Laor model also shows that the line
originates at radii extending from ~10 Schwarzschild radii (r_S) outwards. The
line is direct evidence for the black hole nature of the compact object. The
continuum is well described by dominant disc blackbody emission plus
Comptonized emission. During dipping, spectral evolution is well modelled by
allowing progressive covering of the disc blackbody and simple absorption of
the Comptonized emission showing that the thermal emission is more extended.
Acceptable fits are only obtained by including the disc line in the covering
term, indicating that it originates in the same inner disc region as the
thermal continuum. Dip ingress times and durations are used to provide the
radius of the disc blackbody emitter as 170-370 r_S, and the radius of the
absorber.
