ASCA PV observations of the Seyfert 1 galaxyMCG

ASCA PV observations of the Seyfert 1 galaxy MCG?6?30?15 : rapid variability of the warm absorber. ABSTRACT We present a detailed re-analysis of the two ASCA Performance Veriication observations of the nearby Seyfert 1 galaxy MCG?6?30?15. Connrming the results of Fabian et al. (1994), we nd deenite evidence for the O vii and O viii K-shell absorption edges of the warm absorber and a doubling of the warm absorber column density within the 3 weeks separating the two observations. No intra-day ux-correlated variability of the warm absorber is found. However, we report the discovery of anèvent' 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. (1994), the iron line is broad and strong (equivalent width 300eV). The line proole is also suggestive of it being skewed. Such a line would be expected from a relativistic accretion disk. We also nd very rapid primary X-ray variability. Assuming relativistic beaming to be unimportant, the derived eeciency is comparable to the maximum obtainable from accretion onto a Schwarzschild black hole. Correlated variability outside of the energy range of ASCA might exceed this maximum, thus requiring eecient accretion onto a Kerr hole.