Extreme warm absorber variability in the Seyfert galaxy Mrk 704

¹ Dipartimento di FisicaUniversità degli Studi Roma Tre, via della Vasca Navale 84, 00146 Roma, Italy
e-mail: matt@fis.uniroma3.it
² INAF - Osservatorio Astronomico di Brera, via E. Bianchi 46, 23907 Merate, Italy
³ European Space Astronomy Center of ESA, Apartado 50727, 28080 Madrid, Spain
⁴ M.I.T. Kavli Institute for Astrophysics and Space Research, Cambridge, USA
⁵ INAF-IASF Bologna, via Gobetti 101, 40129 Bologna, Italy
⁶ Astronomical Institute, Academy of Sciences, Bocni II 1401, 14131 Prague, Czech Republic
⁷ Centro de Astrobiología (CSIC-INTA) LAEFF, PO Box 78, Villanueva de la Cañada, Madrid 28691, Spain
⁸ UJF-Grenoble 1/CNRS-INSU, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG) UMR 5274, 38041 Grenoble, France
⁹ INAF - Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio Catone, Roma, Italy
¹⁰ School of Physics and Astronomy, University of Southampton, Highfield, Southampton SO17 1BJ, UK

Received: 5 January 2011
Accepted: 5 July 2011

Abstract

Context. In about half of the 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.

Aims. The aim of this paper is to constrain the warm absorber further by studying its variability.

Methods. We analyzed the X-ray spectra of a Seyfert 1 galaxy, Mrk 704, which was observed twice, three years apart, by XMM-Newton.

Results. The spectra were well fitted with a two-zones absorber, which possibly covers the source only partially. 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 is possibly composed of orbiting clouds in the surroundings of the nucleus, similarly to what was already found in other sources, most notably NGC 1365.