Multiwavelength campaign on Mrk 509

XII. Broad band spectral analysis

¹ UJF-Grenoble 1/CNRS-INSU, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG) UMR 5274, 38041 Grenoble, France
e-mail: pierre-olivier.petrucci@obs.ujf-grenoble.fr
² ISDC Data Centre for Astrophysics, Astronomical Observatory of the University of Geneva, 16 Ch. d’Ecogia, 1290 Versoix, Switzerland
³ Université de Toulouse, UPS-OMP, IRAP, Toulouse, France
⁴ CNRS, IRAP, 9 Av. colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France
⁵ SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
⁶ Sterrenkundig Instituut, Universiteit Utrecht, PO Box 80000, 3508 TA Utrecht, The Netherlands
⁷ INAF – IASF Bologna, via Gobetti 101, 40129 Bologna, Italy
⁸ School of Physics and Astronomy, University of Southampton, Highfield, Southampton SO17 1BJ, UK
⁹ Centro de Astrobiología (CSIC-INTA), Dep. de Astrofísica; LAEFF, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain
¹⁰ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
¹¹ Department of Physics and Astronomy, The John Hopkins University, Baltimore, MD 21218, USA
¹² Instituto de Astronomía, Universidad Católica del Norte, Avenida Angamos 0610, Casilla 1280, Antofagasta, Chile
¹³ Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH, UK
¹⁴ Dipartimento di Fisica, Università degli Studi Roma Tre, via della Vasca Navale 84, 00146 Roma, Italy
¹⁵ Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey, RH5 6NT, UK
¹⁶ Centrum Astronomiczne im. M. Kopernika, Rabiańska 8, 87-100 Toruń, Poland

Received: 6 July 2012
Accepted: 23 September 2012

Abstract

The origin of the different spectral components present in the high-energy (UV to X-rays/gamma-rays) spectra of Seyfert galaxies is still being debated a lot. One of the major limitations, in this respect, is the lack of really simultaneous broad-band observations that allow us to disentangle the behavior of each component and to better constrain their interconnections. The simultaneous UV to X-rays/gamma rays data obtained during the multiwavelength campaign on the bright Seyfert 1 Mrk 509 are used in this paper and tested against physically motivated broad band models.

Mrk 509 was observed by XMM-Newton and INTEGRAL in October/November 2009, with one observation every four days for a total of ten observations. Each observation has been fitted with a realistic thermal Comptonization model for the continuum emission. Prompted by the correlation between the UV and soft X-ray flux, we used a thermal Comptonization component for the soft X-ray excess. We also included a warm absorber and a reflection component, as required by the precise studies previously done by our consortium. The UV to X-ray/gamma-ray emission of Mrk 509 can be well fitted by these components. The presence of a relatively hard high-energy spectrum points to the existence of a hot (kT ~ 100 keV), optically-thin (τ ~ 0.5) corona producing the primary continuum. In contrast, the soft X-ray component requires a warm (kT ~ 1 keV), optically-thick (τ ~ 10−20) plasma.

Estimates of the amplification ratio for this warm plasma support a configuration relatively close to the “theoretical” configuration of a slab corona above a passive disk. An interesting consequence is the weak luminosity-dependence of its emission, which is a possible explanation of the roughly constant spectral shape of the soft X-ray excess seen in AGNs. The temperature (~3 eV) and flux of the soft-photon field entering and cooling the warm plasma suggests that it covers the accretion disk down to a transition radius R_in of 10 − 20 R_g. This plasma could be the warm upper layer of the accretion disk.

In contrast, the hot corona has a more photon-starved geometry. The high temperature (~100 eV) of the soft-photon field entering and cooling it favors a localization of the hot corona in the inner flow. This soft-photon field could be part of the comptonized emission produced by the warm plasma. In this framework, the change in the geometry (i.e. R_in) could explain most of the observed flux and spectral variability.