An absorption event in the X-ray light curve of NGC 3227 |
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| Authors: | G Lamer P Uttley I M MHardy |
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| Institution: | Astrophysikalisches Institut Potsdam, An der Sternwarte 16, D-14482, Potsdam, Germany;Department of Physics and Astronomy, The University, Southampton SO17 1BJ |
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| Abstract: | We have monitored the Seyfert galaxy NGC 3227 with the Rossi X-ray Timing Explorer ( RXTE ) since 1999 January. During late 2000 and early 2001 we observed an unusual hardening of the 2–10 keV X-ray spectrum which lasted several months. The spectral hardening was not accompanied by any correlated variation in flux above 8 keV. We therefore interpret the spectral change as transient absorption by a gas cloud of column density 2.6 × 1023 cm−2 crossing the line of sight to the X-ray source. A spectrum obtained by XMM–Newton during an early phase of the hard-spectrum event confirms the obscuration model and shows that the absorbing cloud is only weakly ionized. The XMM–Newton spectrum also shows that ∼10 per cent of the X-ray flux is not obscured, but this unabsorbed component is not significantly variable and may be scattered radiation from a large-scale scattering medium. Applying the spectral constraints on the cloud ionization parameter and assuming that the cloud follows a Keplerian orbit, we constrain the location of the cloud to be R ∼ 10–100 light-days from the central X-ray source, and its density to be n H∼ 108 cm−3 , implying that we have witnessed the eclipse of the X-ray source by a broad line region cloud. |
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| Keywords: | galaxies: individual: NGC 3227 galaxies: Seyferts X-rays: galaxies |
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