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Rapid X-ray spectral variability in NGC 3227
Ptak, A.; Yaqoob, T.; Serlemitsos, P. J.; Mushotzky, R.; Otani, C.
AA(NASA. Goddard Space Flight Center, Greenbelt, MD, US), AB(NASA. Goddard Space Flight Center, Greenbelt, MD, US), AC(NASA. Goddard Space Flight Center, Greenbelt, MD, US), AD(NASA. Goddard Space Flight Center, Greenbelt, MD, US), AE(Institute of Space and Astronautical Science, Kanagawa, Japan)
Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X), vol. 436, no. 1, p. L31-L34 (ApJL Homepage)
Publication Date:
NASA/STI Keywords:
Active Galactic Nuclei, Ionization, Seyfert Galaxies, X Ray Absorption, X Ray Spectra, Absorption Spectra, Variability
Bibliographic Code:


We present preliminary results of an ASCA observation of the Seyfert 1 galaxy, NGC 3227. The source exhibits rapid X-ray amplitude and spectral variability, the flux below 2 keV varying by a factor of approximately 3 in approximately 10,000 s while the flux in the 2-10 keV band varies by a factor of approximately 2 in the same interval. The spectrum below approximately 1 keV shows complex structure compared to a simple power-law model. We argue that the simplest interpretation of the spectrum is in terms of a power-law continuum modified by absorption in a photoionized medium. Simple, static, ionized absorber models yield an ionization parameter of approximately 0.05 and column density approximately 3.6 x 1021/sq cm. However, the data strongly indicate that the situation is much more complex than this. If the spectral variability is caused by a changing ionization state of the absorber, then both the ionization state and column density are required to decrease as the intrinsic source luminosity increases. This does not have a simple physical interpretation. On the other hand, the data are also consistent with the spectral variability being due to changes in the intrinsic power-law index with little change in the ionization state of the absorber. This case could correspond to an absorber which is always in some average ionization state and the continuum variability is too fast for the absorber to deviate significantly from that, or the absorber could be in the form of an X-ray-heated wind.

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