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Register a new userRelativistic Broadening of Iron Emission Lines in a Sample of AGN
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Laura W. Brenneman
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We present a uniform X-ray spectral analysis of eight type-1 active galactic nuclei (AGN) that have been previously observed with relativistically broadened iron emission lines. Utilizing data from the XMM-Newton European Photon Imaging Camera (EPIC-pn) we carefully model the spectral continuum, taking complex intrinsic absorption and emission into account. We then proceed to model the broad Fe K feature in each source with two different accretion disk emission line codes, as well as a self-consistent, ionized accretion disk spectrum convolved with relativistic smearing from the inner disk. Comparing the results, we show that relativistic blurring of the disk emission is required to explain the spectrum in most sources, even when one models the full reflection spectrum from the photoionized disk.
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Broad iron emission lines are observed in many accreting systems from black holes in AGN and X-ray binaries to neutron star low-mass X-ray binaries. The origin of the line broadening is often interpreted as due to dynamical broadening and relativistic effects. However, alternative interpretations have been proposed, included broadening due to Compton scattering in a wind or accretion disk atmosphere. Here we explore the observational signatures expected from broadening in a wind, in particular that the iron line width should increase with an increase in the column density of the absorber (due to an increase in the number of scatterings). We study the data from three neutron star low-mass X-ray binaries where both a broad iron emission line and absorption lines are seen simultaneously, and show that there is no significant correlation between line width and column density. This favors an inner disk origin for the line broadening rather than scattering in a wind.
Accretion models predict that fluorescence lines broadened by relativistic effects should arise from reflection of X-ray emission onto the inner region of the accretion disc surrounding the central black hole of active galactic nuclei (AGN). The theory behind the origin of relativistic lines is well established, and observational evidence from a moderate number of sources seems to support the existence of these lines. The aim of this work is to establish the fraction of AGN with relativistic Fe Kalpha lines, and study possible correlations with source physical properties. An XMM-Newton collection of 149 radio-quiet Type 1 AGN has been systematically and uniformly analyzed in order to search for significant evidence of a relativistically broadened Fe Kalpha line. To enable statistical studies, an almost complete, flux-limited subsample of 31 sources has been defined. The 2-10 keV spectra of the FERO sources have been compared with a complex model including most of the physical components observed in the X-ray spectra of Seyfert galaxies: a power law primary continuum modified by non-relativistic Compton reflection and warm absorption, plus a series of narrow Fe line reflection features. The observed fraction of sources in the flux-limited sample that show significant evidence of a relativistic Fe Kalpha line is 36%. The average line Equivalent Width (EW) is of the order of 100 eV, while the average disc inclination angle is 28+/-5 deg and the average power-law index of the radial disc emissivity law is 2.4+/-0.4. The spin value is well constrained only in 2 cases (MCG-6-30-15 and MRK509), and in the rest of the cases, whenever a constraint can be placed, it always implies the rejection of the static black hole solution. The Fe Kalpha line EW does not correlate with disc parameters or with system physical properties, such as black hole mass, accretion rate and hard X-ray luminosity.
During the September-October 2008 outburst of the accreting millisecond pulsar SAX J1808.4-3658, the source was observed by both Suzaku and XMM-Newton approximately 1 day apart. Spectral analysis reveals a broad relativistic Fe K-alpha emission line which is present in both data-sets, as has recently been reported for other neutron star low-mass X-ray binaries. The properties of the Fe K line observed during each observation are very similar. From modeling the Fe line, we determine the inner accretion disk radius to be 13.2 +/- 2.5 GM/c^2. The inner disk radius measured from the Fe K line suggests that the accretion disk is not very receded in the island state. If the inner disk (as measured by the Fe line) is truncated at the magnetospheric radius this implies a magnetic field strength of ~3E8 G at the magnetic poles, consistent with other independent estimates.
Initial results on the iron K-shell line and reflection component in several AGN observed as part of the Suzaku Guaranteed time program are reviewed. This paper discusses a small sample of Compton-thin Seyferts observed to date with Suzaku; namely MCG -5-23-16, MCG -6-30-15, NGC 4051, NGC 3516, NGC 2110, 3C 120 and NGC 2992. The broad iron K$alpha$ emission line appears to be present in all but one of these Seyfert galaxies, while the narrow core of the line from distant matter is ubiquitous in all the observations. The iron line in MCG -6-30-15 shows the most extreme relativistic blurring of all the objects, the red-wing of the line requires the inner accretion disk to extend inwards to within 2.2Rg of the black hole, in agreement with the XMM-Newton observations. Strong excess emission in the Hard X-ray Detector (HXD) above 10 keV is observed in many of these Seyfert galaxies, consistent with the presence of a reflection component from reprocessing in Compton-thick matter (e.g. the accretion disk). Only one Seyfert galaxy (NGC 2110) shows neither a broad iron line nor a reflection component. The spectral variability of MCG -6-30-15, MCG -5-23-16 and NGC 4051 is also discussed. In all 3 cases, the spectra appear harder when the source is fainter, while there is little variability of the iron line or reflection component with source flux. This agrees with a simple two component spectral model, whereby the variable emission is the primary power-law, while the iron line and reflection component remain relatively constant.
The detection of gravitationally redshifted optical emission lines has been reported just for a few active galaxies. In this paper we give a short overview of studies that analyzed or exploited the detection of the gravitational redshift in optical AGN spectra. In addition, we tested the consistency of gravitational redshift as the physical origin of the redward shifts observed in their spectra using a sample of $approx$ 50 Hamburg-ESO intermediate to high redshift quasars that are among the most luminous quasars known ($10^{47} lesssim L lesssim 10^{48}$ erg/s), and are expected to host very massive black holes. To this aim we modeled the line profile with accretion disk models around a black hole.
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