The X‐Ray Spectral Variability of the Seyfert Galaxy NGC 3227

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Abstract
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 Γ ~ 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 3×1021 cm-2 of ionized material with an X-ray ionization parameter UX 0.01. Both the column and ionization state of this material are at the low end of the distribution of parameters observed for Seyfert 1 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~few×1020 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 ΔΓ 0.1 during a flare of duration ~104 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 ~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 ~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.
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