EDP Sciences
Free access
Volume 431, Number 1, February III 2005
Page(s) 97 - 102
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20041690

A&A 431, 97-102 (2005)
DOI: 10.1051/0004-6361:20041690

Simultaneous X-ray and optical spectroscopy of the Seyfert galaxy Mrk 993

A. Corral, X. Barcons, F. J. Carrera, M. T. Ceballos and S. Mateos

Instituto de Física de Cantabria (CSIC-UC), 39005 Santander, Spain
    e-mail: corralra@ifca.unican.es

(Received 19 July 2004 / Accepted 12 October 2004)

We present the results of simultaneous XMM-Newton X-ray and 3.5 m/CAHA optical spectroscopic observations of the Seyfert galaxy Mrk 993. This galaxy exhibited in the past significant variations of its broad emission lines which classified it as Sy1, Sy1.5 and Sy1.9 in different epochs. In order to test the X-ray/optical consistency of the unified AGN model we have compared the amount of photoelectric X-ray absorption with the Balmer decrement of broad emission line components. The optical data show that during our observations Mrk 993 was in a Sy1.8 state with a Balmer decrement of $\sim $9. The X-ray absorbing gas amounts only to $7\times10^{20}\,
{\rm cm}^{-2}$ , most likely due to the host galaxy. For a normal gas to dust ratio in the absorbing material (expected to arise in the molecular torus) both quantities are clearly discrepant with an intrinsic Balmer decrement of  $\sim $3.4. We therefore conclude that the Balmer ratio is intrinsic rather than produced by obscuration and therefore that in this object the optical broad line emission properties are dictated by the physics of the broad line region rather than orientation/obscuration effects.

Key words: galaxies: active -- galaxies: Seyfert -- X-rays: galaxies

© ESO 2005