XMM-Newton observation of the Seyfert 1.8 ESO 113-G010: Discovery of a highly redshifted iron line at 5.4 keV

¹ Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, 85741 Garching, Germany e-mail: dporquet@mpe.mpg.de
² Laboratory for High Energy Astrophysics, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
³ Universities Space Research Association, 7501 Forbes Boulevard, Suite 206, Seabrook, MD 20706, USA
⁴ Joint Center for Astrophysics, Physics Department, University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250, USA

Received: 2 June 2004
Accepted: 17 July 2004

Abstract

We present a spectral analysis of the Seyfert 1.8 ESO 113-G010 observed with XMM-Newton for 4 ks. The spectrum shows a soft excess below 0.7 keV and more interestingly a narrow emission Gaussian line at 5.4 keV (in its rest-frame), most probably originating from a redshifted iron Kα line. No significant line at or above 6.4 keV is found contrary to other objects showing redshifted lines, ruling out a strong blue-wing to the line profile. The line is detected at 99% confidence, from performing Monte Carlo simulations which fully account for the range of energies where a narrow iron line is likely to occur. The energy of the line could indicate emission from relativistic (0.17–0.23 c) ejected matter moving away from the observer, as proposed for Mrk 766 by Turner et al. ([CITE], ApJ, 603, 62). Alternatively, the emission from a narrow annulus at the surface of the accretion disk is unlikely due to the very small inclination angle (i.e. less than 10°) required to explain the narrow, redshifted line in this intermediate Seyfert galaxy. However emission from a small, localized hot-spot on the disk, occurring within a fraction of a complete disk orbit, could also explain the redshifted line. This scenario would be directly testable in a longer observation, as one would see significant variations in the energy and intensity of the line within an orbital timescale.