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abstract
Variability of the main spectral features of MCG -6-30-15 is demonstrated in all four Ginga observations. Temporal and spectral analysis reveal timescales from hours to years, and there are no apparent delays in most of the features.
The absence of delays can be the result of absorbing material in the line of sight. Partial covering by a cold absorber gives a poor fit, as does complete coverage by a warm absorber. We therefore assume that a flat power-law source is partially covered by a warm absorber, and achieve a significant improvement in the fits. Our best fit parameters suggest that a geometrically thin warm absorber, in which only the Fe is not completely ionized, lies in a region between the central engine and the Broad Line Region.
Our results are supported by the ASCA observation of an $O_{VII}$ edge energy which does not vary with flux, as would be expected in the case that only a fraction of the Oxigen in the absorber is not completely ionized. The apparent discrepancy of Ginga results with ASCA and Rosat results that was previously reported is eliminated, because no cold absorption is needed.
