Abstract
In about half of Seyfert galaxies, the X-ray emission is absorbed by an optically thin, ionized medium, the so-called "Warm Absorber", whose origin and location is still a matter of debate. The aims of this paper is to put more constraints on the warm absorber by studying its variability. We analyzed the X-ray spectra of a Seyfert 1 galaxy, Mrk 704, which was observed twice, three years apart, by XMM-Newton. The spectra were well fitted with a two zones absorber, possibly covering only partially the source. The parameters of the absorbing matter - column density, ionization state, covering factor - changed significantly between the two observations. Possible explanations for the more ionized absorber are a torus wind (the source is a polar scattering one) or, in the partial covering scenario, an accretion disk wind. The less ionized absorber may be composed of orbiting clouds in the surroundings of the nucleus, similarly to what already found in other sources, most notably NGC 1365.
Highlights
Absorption from ionized matter in the X-ray spectrum of AGN was discovered many years ago (Halpern 1984)
The paper is organized as follows: in Sect. 2 we report on the XMM-Newton observations and data reduction, while the relative data analysis is discussed in Sect
The very similar hard X-ray spectrum in the two observations together with the change in the column density suggest that the variations are caused by a change in the properties of the absorbing clouds
Summary
Absorption from ionized matter in the X-ray spectrum of AGN (the so-called warm absorber) was discovered many years ago (Halpern 1984). Mrk 704 is a local (z = 0.029234) Seyfert 1.2 galaxy (Veron-Cetty & Veron 2010), bright enough in X-rays to be detected by Swift/BAT (Ajello et al 2008). In this paper we report on extreme warm absorber variability on yearly time scales, revealed by two XMM-Newton observations, and possible variability on monthly time scales from short Swift/XRT observations. 2 we report on the XMM-Newton observations and data reduction, while the relative data analysis is discussed in Sect. 3. Section 4 presents the analysis of the Swift and ASCA observations, while the results are summarized and discussed in Sect.
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