Fe K emission and absorption features in XMM-Newton spectra of Markarian 766: evidence for reprocessing in flare ejecta
journal contributionposted on 03.11.2006, 13:23 by Kenneth A. Pounds, J.N. Reeves, Kim L. Page, Graham A. Wynn, Paul T. O'Brien
We report on the analysis of a long XMM–Newton European Photon Imaging Camera (EPIC) observation in 2001 May of the narrow-line Seyfert 1 galaxy Markarian 766 (Mrk 766). The 3–11 keV spectrum exhibits a moderately steep power-law continuum, with a broad emission line at 6.7 keV, probably blended with a narrow line at 6.4 keV, and a broad absorption trough above 8.7 keV. We identify both broad spectral features with reprocessing in He-like Fe. An earlier XMM–Newton observation of Mrk 766 in 2000 May, when the source was a factor 2 fainter, shows a similar broad emission line, but with a slightly flatter power law and absorption at a lower energy. In neither observation do we find a requirement for the previously reported broad 'red wing' to the line and hence of reflection from the innermost accretion disc. More detailed examination of the longer XMM–Newton observation reveals evidence for rapid spectral variability in the Fe K band, apparently linked with the occurrence of X-ray 'flares'. A reduction in the emission line strength and increased high-energy absorption during the X-ray flaring suggests that these transient effects are due to highly ionized ejecta associated with the flares. Simple scaling from the flare avalanche model proposed for the luminous quasi-stellar object PDS 456 confirms the feasibility of coherent flaring being the cause of the strong peaks seen in the X-ray light curve of Mrk 766.