Volume 534, October 2011
|Number of page(s)||14|
|Published online||29 September 2011|
Multiwavelength campaign on Mrk 509
IV. Optical-UV-X-ray variability and the nature of the soft X-ray excess
Mullard Space Science Laboratory, University College London,
Holmbury St. Mary, Dorking,
2 SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
3 Sterrenkundig Instituut, Universiteit Utrecht, PO Box 80000, 3508 TA Utrecht, The Netherlands
4 UJF-Grenoble 1/CNRS-INSU, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG) UMR 5274, 38041 Grenoble, France
5 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
6 Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD 21218, USA
7 School of Physics and Astronomy, University of Southampton, Highfield, Southampton, SO17 1BJ, UK
8 Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA, UK
9 ISDC, Geneva Observatory, University of Geneva, Ch. d’Écogia 16, 1290 Versoix, Switzerland
10 INAF-IASF Bologna, via Gobetti 101, 40129 Bologna, Italy
11 Instituto de Astronomía, Universidad Católica del Norte, Avenida Angamos 0610, Casilla 1280, Antofagasta, Chile
12 Department of Physics, University of Oxford, Keble Road, Oxford, OX1 3RH, UK
Accepted: 10 June 2011
We present the analysis of XMM-Newtonand Swiftoptical-UV and X-ray observations of the Seyfert-1/QSO Mrk 509, part of an unprecedented multi-wavelength campaign, investigating the nuclear environment of this AGN. The XMM-Newtondata are from a series of 10 observations of about 60 ks each, spaced from each other by about 4 days, taken in Oct.-Nov. 2009. During our campaign, Mrk 509 was also observed with Swiftfor a period of about 100 days, monitoring the behaviour of the source before and after the XMM-Newtonobservations. With these data we have established the continuum spectrum in the optical-UV and X-ray bands and investigated its variability on the timescale of our campaign with a resolution time of a few days. In order to measure and model the continuum as far as possible into the UV, we also made use of Hubble Space Telescope (HST) cosmic origin spectrograph (COS) observations of Mrk 509 (part of our coordinated campaign) and of an archival Far Ultraviolet Spectroscopic Explorer (FUSE) observation. We have found that in addition to an X-ray power-law, the spectrum displays soft X-ray excess emission below 2 keV, which interestingly varies in association with the thermal optical-UV emission from the accretion disc. The change in the X-ray power-law component flux (albeit smaller than that of the soft excess), on the other hand, is uncorrelated to the flux variability of the soft X-ray excess and the disc component on the probed timescale. The results of our simultaneous broad-band spectral and timing analysis suggest that, on a resolution time of a few days, the soft X-ray excess of Mrk 509 is produced by the Comptonisation of the thermal optical-UV photons from the accretion disc by a warm (0.2 keV) optically thick (τ ~ 17) corona surrounding the inner regions of the disc. This makes Mrk 509, with a black hole mass of about 1–3 × 108 M⊙, the highest mass known system to display such behaviour and origin for the soft X-ray excess.
Key words: galaxies: active / galaxies: nuclei / galaxies: Seyfert / quasars: individual: Mrk 509 / X-rays: galaxies
© ESO, 2011
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