The X-ray Spectral Variability of the Seyfert Galaxy NGC 3227

Abstract

(Abridged) We present the results from {\it ASCA} observations of NGC 3227 along with those from a {\it ROSAT} observation. The 0.6--10 keV continuum is consistent with a powerlaw with $\hat{I}“\sim 1.6$, flatter than that typically observed in Seyfert galaxies. Fe $K$-shell emission is observed with an EW and profile typical of Seyfert 1 galaxies. The {\it ASCA} observations in 1993 reveal absorption by a screen $N_{H,z}^{ion} \simeq 3\times10^{21} cm^{-2}}$ of ionized material with $U_X\simeq 0.01$. Joint analysis of the {\it ASCA} and {\it ROSAT} data show an additional screen of neutral material instrinsic to NGC 3227 with $N_{H,z}^{neu}\sim$few$\times10^{20} cm^{-2}}$. NGC 3227 exhibits spectral variability both within and between the observations, due to short-term variability in the continuum emission and longer-term variability in the absorption. Time-resolved spectroscopy show the continuum steepened by $\hat{I}”\hat{I}“\simeq 0.1$ during a flare of duration $\sim 10^4$s. The column increased by a factor of $\sim 10$ 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 $\sim$10% of the nuclear emission to escape without attenuation.

Accepted for publn in ApJ. LaTeX, 38 pages (inc 7 figs) & a PS file w/ 4 tables. For full abstract and other download options, see href="http://lheawww.gsfc.nasa.gov/~george/papers/3227/abstract.html