We present broad-band ( 2 keV to 2 MeV ) x-ray spectra of GRO J1655–40 , a luminous X-ray transient and occasional source of relativistic radio jets , obtained with the Rossi X-Ray Timing Explorer ( RXTE ) and the Oriented Scintillation Spectrometer Experiment ( OSSE ) .
In one observation , the luminosity is found to be 18 % of the Eddington limit , which is one of the highest luminosities ever observed from GRO J1655–40 .
For this observation , we find that an adequate fit is obtained when a broad iron line and a reflection component are added to a model consisting of a power-law plus a soft excess component .
The 95 % confidence lower limit on the rms line width is 0.86 keV .
The power-law component has a photon index of 2.72 ^ { +0.03 } _ { -0.08 } and extends to at least 800 keV without a cutoff .

After this observation , a significant drop in the ( 5-12 keV ) / ( 1.5-5 keV ) hardness ratio occured on a timescale less than 2 hours .
From an RXTE observation of GRO J1655–40 made after the hardness transition , we find that the power-law index is harder ( \alpha = 2.415 \pm 0.011 ) , the flux of the power-law component is lower , and the total luminosity is 10 % of the Eddington limit .
The change in the power-law component is consistent with the correlation between the spectral index and power-law flux previously reported for GRO J1655–40 .