Suzaku broad-band observations of the Seyfert 1 galaxies Mrk 509 and Mrk 841

¹ LUTH, Observatoire de Paris, CNRS, Université Paris Diderot, 5 place Jules Janssen, 92190 Meudon, France
e-mail: matteo.cerruti@obspm.fr
² School of Physics and Astronomy, University of Southampton, Highfield, Southampton SO17 1BJ, UK
³ SRON, Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
⁴ MIT, Kavli Institute for Astrophysics and Space Research, 77 Massachusetts Avenue, NE80-6011, Cambridge, MA, 02139, USA
⁵ Dipartimento di Fisica, Università degli Studi Roma Tre, via della Vasca Navale 84, 00146 Roma, Italy
⁶ APC, Université de Paris 7 Denis Diderot, 75205 Paris Cedex, France
⁷ UJF-Grenoble 1/CNRS-INSU, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG), UMR 5274, 38041 Grenoble, France

Received: 5 January 2011
Accepted: 22 August 2011

Abstract

Context. Markarian 509 and Markarian 841 are two bright Seyfert 1 galaxies with X-ray spectra characterised by a strong soft excess and a variable Fe Kα line, as shown by several X-ray observatories in the past.

Aims. We report an analysis and modelling of new Suzaku observations of these sources, taken between April and November, 2006, for Mrk 509, and between January and July, 2007, for Mrk 841, for a total exposure time of  ≈ 100 ks each. Data from XIS and HXD/PIN instruments, going from 0.5 to 60 keV, represent the highest spectral resolution simultaneous broad-band X-ray spectrum for these objects, and provide the strongest constraints yet on the origin of the soft excess emission.

Methods. We fitted the broad-band spectrum of both sources with a double Comptonisation model, adding neutral reflection from distant material and a two-phase warm absorber. We then studied the two competing models developed to explain the soft excess in terms of atomic processes: a blurred ionised disc reflection and an ionised absorption by a high velocity material.

Results. When fitting the data in the 3–10 keV range with a power law spectrum, and extrapolating this result to low energies, a soft excess is clearly observed below 2 keV, although its strength is weak compared to previous observations of both sources. A moderate hard excess is seen at energies higher than 10 keV, together with a neutral Fe Kα narrow emission line at E₀ ≈ 6.4 keV and a broad Fe emission line. For Mrk 509, the broad Fe emission line is required in all the three physical models to ensure a good fit to the data: this finding suggests that the blurred reflection model correctly describes the soft excess, but that it underestimates the broad Fe emission line. For the smeared absorption model, this suggests instead that the continuum spectrum absorbed by the outflowing gas should indeed contain a reflected component. For Mrk 841, all three models that we tested provide a good fit to the data, and we cannot rule out any of them. A broad emission line is required in the double Comptonisation and smeared absorption models, while the blurred reflection model consistently fits the broad-band spectrum, without adding any extra emission-line component.