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

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 similar to 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 OVII 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 similar to 5 x 10(20) cm(-2). The absorption spectrum can be modeled by two distinct gas components (log xi 0.47 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.