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publication

ASCA PV observations of the Seyfert 1 galaxy MCG-6-30-15: rapid variability of the warm absorber

C. S. Reynolds, A. C. Fabian, K. Nandra, H. Inoue, H. Kunieda and K. Iwasawa

Abstract

We present a detailed re-analysis of the two ASCA Performance Verification observations of the nearby Seyfert 1 galaxy MCG-6-30-15. Confirming the results of Fabian et al. (1994), we find definite evidence for the OVII and OVIII K-shell absorption edges of the warm absorber and a doubling of the warm absorber column density within the three weeks separating the two observations. No intraday flux-correlated variability of the warm absorber is found. However, we report the discovery of an `event' in which the warm absorber parameters temporarily change for ~10000s before returning to their original values. Possible interpretations are discussed, but a contradiction remains: the constancy of the ionization state of the warm absorber argues that it lies at large distances from the central source, whereas the short-term change in column density argues for small distances. Fluorescent iron emission is examined. As found by Fabian et al., the iron line is broad and strong (equivalent width ~300 eV). The line profile is also suggestive of it being skewed. Such a line would be expected from a relativistic accretion disc. We also find very rapid primary X-ray variability. Assuming relativistic beaming to be unimportant, the derived efficiency is comparable to the maximum obtainable from accretion on to a Schwarzschild black hole. Correlated variability outside of the energy range of ASCA might exceed this maximum, thus requiring efficient accretion on to a Kerr hole.

 
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