Iron-line and continuum flux variations in the RXTE spectra of the black hole candidate XTE J1650-500

We present the results of spectral fits made to 57 pointed observations of the Galactic black hole candidate and X-ray transient XTE J1650-500, made with the Rossi X-ray Timing Explorer (RXTE) in 2001 when the source was in a transition from the hard state to the soft state. A strong and variable Fe K alpha emission line is detected in these spectra. The line flux varies in a non-linear way with the hard X-ray flux, in apparent contradiction to the predictions of simple disc reflection models. We observe a change in the overall trend that coincides with changes in the continuum X-ray spectrum and the fast X-ray variability. The Fe-line flux versus hard X-ray flux variations are consistent with the predictions of reflection models that consider high disc-ionization states and with a model that considers gravitational light-bending effects. Indications for an anticorrelation between the Fe-line flux and the hard X-ray flux in the spectrally hardest observations and weak variations in the Fe-line energy (as observed with XMM-Newton and BeppoSAX) slightly favour the light-bending interpretation.