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Astron. Astrophys. 327, 483-492

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Evidence for a dusty warm absorber in NGC 3227?

Stefanie Komossa and Henner FinkFORMULA

Max-Planck-Institut für extraterrestrische Physik, D-85740 Garching, Germany

Received 11 December 1996 / Accepted 19 June 1997


We have analyzed survey and pointed ROSAT PSPC observations of the Seyfert galaxy NGC 3227. Large amplitude X-ray variability is detected, with a factor FORMULA 15 change in count rate within about 3 years. Smaller changes are seen on the timescale of days, the largest being a factor of 3.5. No strong spectral variability is found throughout the pointed observation. The X-ray spectrum is modeled in terms of warm absorption and both, a dust-free warm absorber and one with internal dust, give an excellent spectral fit. Additionally using multi-wavelength observations of NGC 3227, the dusty warm absorber is favored and suggested as an explanation for the lack of a large cold absorbing column in the soft X-ray region despite excess reddening along the line of sight. Self-consistent re-calculation of the models including Galactic-ISM-like dust results in an ionization parameter FORMULA and a column density FORMULA of the warm absorber. X-ray variability and dust survival arguments are used to constrain the density and further properties of the ionized material. The influence of dust and other parameters on the thermal stability of the warm absorber is investigated. Predictions are given for the absorber-intrinsic optical-UV line emission and absorption.

Key words: galaxies: active - individual: NGC 3227 - emission lines - Seyfert - X-rays: galaxies

Send offprint requests to: St. Komossa, (skomossa@mpe-garching.mpg.de)
FORMULA deceased in Dec. 1996

© European Southern Observatory (ESO) 1997

Online publication: October 14, 1997
Last change: April 6, 1998