Open AccessAn absorption event in the X‐ray light curve of NGC 3227
Author(s) -
Lamer G.,
Uttley P.,
M I. M.
Publication year - 2003
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2003.06759.x
Subject(s) - physics , astrophysics , line of sight , ionization , spectral line , flux (metallurgy) , galaxy , light curve , astronomy , line (geometry) , absorption (acoustics) , scattering , optics , ion , materials science , geometry , mathematics , quantum mechanics , metallurgy
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 × 10 23 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 ∼ 10 8 cm −3 , implying that we have witnessed the eclipse of the X‐ray source by a broad line region cloud.