SIMBAD references

We have analyzed Ginga data collected during the peak of the outburst of the black-hole candidate GS 2023+338. The X-ray spectrum contains a strong iron emission line with an energy of ∼6.4keV, sometimes completely dominating the spectrum. The X-ray intensity shows very strong fluctuations. However, the fluctuations in the iron line are much weaker than those in the continuum. We find a [0.01-8Hz] fractional rms variability of 7±15% in the iron flux, as compared to a value of 60% for the continuum. Only on time scales longer than 200s does the iron line show a comparable level of variability as the continuum. The lack of variability on time scales below 200s suggests that the size of the iron line emitting region is of the order of 10² lt s. We conclude that the iron line is not formed in the inner region of the accretion disk, which is the likely region where the variability in the continuum originates.