The X-ray spectral variability of the Seyfert galaxy NGC 3227

We present the results from ASCA observations of NGC 3227 performed during 1993 and 1995, along with those from a ROSAT observation performed pseudosimultaneously with the former. We find the 0.6-10 keV continuum to be consistent with a power law with a photon index Gamma similar to 1.6, flatter than that typically observed in Seyfert galaxies confirming previous results. Significant Fe K-shell emission is observed during both epochs, with an equivalent width and profile typical of Seyfert 1 galaxies. The ASCA observations in 1993 reveal absorption by a screen N-H,z(ion) similar or equal to 3 x 10(21) cm(-2) of ionized material with an X-ray ionization parameter U-X similar or equal to 0.01. Both the column and ionization state of this material are at the low end of the distribution of parameters observed for Seyfert I galaxies. Joint analysis of the ASCA and ROSAT data at this epoch shows an additional screen of neutral material instrinsic to NGC 3227 with N-H,z(neu) similar to few x 10(20) cm(-2). We find NGC 3227 to exhibit significant spectral variability both within and between the observations. The most likely explanation involves short-term variability in the continuum emission and longer term variability in the column density of the ionized material. Time-resolved spectroscopy and color-color analysis indicate that the slope of the continuum steepened by Delta Gamma similar or equal to 0.1 during a hare of duration similar to 10(4) s, within the 1993 observation. However, we were unable to distinguish between a steepening of the "primary" continuum and a change in the relative strengths of the power law and a putative Compton-reflection component. The absorbing column increased by a factor of similar to 10 by the 1995 epoch, while the continuum is consistent with that observed in 1993. The 1995 data also show evidence that the warm absorber allows similar to 10% of the nuclear emission to escape without attenuation. We review our findings in the context of the previous results from this and similar objects and discuss the prospects of future observations.