X-ray/ultraviolet observing campaign of the Markarian 279 active galactic nucleus outflow: a close look at the absorbing/emitting gas with Chandra-LETGS

¹ SRON National Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands e-mail: e.costantini@sron.nl
² Astronomical Institute, Utrecht University, PO Box 80000, 3508 TA, Utrecht, The Netherlands
³ CASA, University of Colorado, 389 UCB, Boulder, CO 80309-0389, USA
⁴ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
⁵ University of Oxford, St John's College Research Centre, Oxford, OX1 3JP, UK
⁶ Department of Physics, Technion, Haifa 32000, Israel
⁷ Department of Physics and Astronomy, University of Nebraska, Lincoln, NE 68588-0111, USA
⁸ Department of Physics, Western Michigan University, Kalamazoo, MI 49008, USA
⁹ Department of Physics, University of Nevada, 4505 South Maryland Parkway, Las Vegas, NV 89154, USA
¹⁰ Department of Physics, Astronomy, and Geosciences, Towson University, Towson, Maryland 21252, USA

Received: 7 April 2006
Accepted: 14 September 2006

Abstract

We present a Chandra-LETGS observation of the Seyfert 1 galaxy Mrk 279. This observation was simultaneous with HST-STIS and FUSE observations, in the context of a multiwavelength study of this source. The Chandra pointings were spread over ten days for a total exposure time of ~360 ks. The maximal continuum flux variation is of the order of 30%. The spectrum of Mrk 279 shows evidence of broad emission features, especially at the wavelength of the O vii triplet. We quantitatively explore the possibility that this emission is produced in the broad line region (BLR). We modeled the broad UV emission lines seen in the FUSE and HST-STIS spectra following the “locally optimally emitting cloud” approach. This method considers the emission from BLR as arising from “clouds” with a wide range of densities and distances from the source. We find that the X-ray lines luminosity derived from the best fit BLR model match the observed X-ray features, suggesting that the gas producing the UV lines is sufficient to account for the X-ray emission. The spectrum is absorbed by ionized gas whose total column density is ~5 10²⁰ cm^-2. The absorption spectrum can be modeled by two distinct gas components (log and 2.49, respectively) both showing a significant outflow velocity. However, the data also allow for the presence of intermediate ionization components. The distribution of the column densities of such extra components as a function of the ionization parameter is not consistent with a continuous, power-law like, absorber, suggesting a complex structure for the gas outflow for Mrk 279.