arXiv subjects

K. L. Page

Publications and source records attributed to K. L. Page.

187 records · Page 11Linked to original sources

arXiv2003

An X-ray Baldwin effect for the narrow Fe K-alpha lines observed in Active Galactic Nuclei

The majority of Active Galactic Nuclei (AGN) observed by XMM-Newton reveal narrow Fe K-alpha lines at ~ 6.4 keV, due to emission from cold (neutral) material. There is an X-ray Baldwin effect in Type I AGN, in that the equivalent width of the line decreases with increasing luminosity, with weighted linear regression giving EW ~ L^{-0.17+/-0.08} (Spearman Rank probability of > 99.9%). With current instrumental capabilities it is not possible to determine the precise origin for the narrow line, with both the Broad Line Region and putative molecular torus being possibilities. A possible explanation for the X-ray Baldwin effect is a decrease in covering factor of the material forming the fluorescence line.

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arXiv2003

Evidence of a high velocity ionised outflow in a second narrow line quasar PG0844+349

Following the discovery of X-ray absorption in a high velocity outflow from the bright quasar PG1211+143 we have searched for similar features in XMM archival data of a second (high accretion rate) quasar PG0844+349. Evidence is found for absorption lines in both the EPIC and RGS spectra, whose identification with resonance transitions in H-like Fe, S, and Ne implies an origin in highly ionised matter with an outflow velocity of order ~0.2c. The line equivalent widths require a line-of-sight column density of N_H ~ 4 x 10^23 cm^-2, at an ionisation parameter of log(xi) ~ 3.7. Assuming a radial outflow being driven by radiation pressure from the inner accretion disc, as suggested previously for PG1211+143, the flow is again likely to be optically thick, in this case within ~ 25 Schwarzschild radii. We suggest that a high velocity, highly ionised outflow is likely to be a significant component in the mass and energy budgets of many AGN accreting at or above the Eddington rate.

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arXiv2003

Fe K emission and absorption features in XMM-Newton spectra of Mkn 766 - evidence for reprocessing in flare ejecta

We report on the analysis of a long XMM-Newton EPIC observation in 2001 May of the Narrow Line Seyfert 1 galaxy Mkn 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 Mkn 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 ionised ejecta associated with the flares. Simple scaling from the flare avalanche model proposed for the luminous QSO PDS 456 (Reeves etal. 2002) confirms the feasibility of coherent flaring being the cause of the strong peaks seen in the X-ray light curve of \mkn.

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arXiv2003

A simultaneous XMM-Newton and BeppoSAX observation of the archetypal Broad Line Seyfert 1 galaxy NGC 5548

We report the spectral analysis of a long XMM-Newton observation of the well-studied, moderate luminosity Broad Line Seyfert 1 galaxy NGC 5548. The source was at an historically average brightness and we find the hard (3-10 keV) spectrum can be well fitted by a power law of photon index gamma ~ 1.75, together with reflection. The only feature in the hard X-ray spectrum is a narrow emission line near 6.4 keV, with an equivalent width of ~ 60 eV. The energy and strength of this line is consistent with fluorescence from `neutral' iron distant from the central continuum source. We find no evidence for a broad Fe K line, with an upper limit well below previous reports, suggesting the inner accretion disc is now absent or highly ionised. The addition of simultaneous BeppoSAX data allows the analysis to be extended to 200 keV, yielding important constraints on the total reflection. Extrapolation of the hard X-ray power law down to 0.3 keV shows a clear `soft excess' below ~ 0.7 keV. After due allowance for the effects of a complex warm absorber, measured with the XMM-Newton RGS, we find the soft excess is better described as a smooth upward curvature in the continuum flux below ~ 2 keV. The soft excess can be modelled either by Comptonised thermal emission or by enhanced reflection from the surface of a highly ionised disc.

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arXiv2003

An XMM-Newton observation of the Narrow Line Seyfert 1 Galaxy, Markarian 896

XMM-Newton observations of the NLS1 Markarian 896 are presented. Over the 2-10 keV band, an iron emission line, close to 6.4 keV, is seen. The line is just resolved and has an equivalent width of ~170 eV. The broad-band spectrum is well modelled by a power law slope of gamma ~ 2.03, together with two blackbody components to fit the soft X-ray excess. Using a more physical two-temperature Comptonisation model, a good fit is obtained for an input photon distribution of kT ~ 60eV and Comptonising electron temperatures of ~0.3 and 200 keV. The soft excess cannot be explained purely through the reprocessing of a hard X-ray continuum by an ionised disc reflector.

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arXiv2002

Serendipitous AGN in the XMM-Newton fields of Markarian 205 and QSO 0130-403

The X-ray spectra of serendipitously observed AGN in the XMM-Newton fields of Mrk 205 and QSO 0130-403 are analysed. The sample consists of 23 objects, none of which is detected at radio frequencies, with a median X-ray luminosity of ~ 4 x 10^44 erg s^-1 and redshifts ranging from ~0.1 to just over 3. The mean photon index was found to be 1.89 +/- 0.04. In contrast to past ASCA and ROSAT observations of high-redshift radio-loud quasars, we find little evidence for excess intrinsic absorption in these radio-quiet objects, with only three sources requiring a column density in excess of the Galactic value. Comparing the measured spectral indices over the redshift range, we also find there is no X-ray spectral evolution of QSOs with time, up to redshift 3. Within the sample there is no evidence for evolution of the optical to X-ray spectral index, alpha-ox, with redshift, the mean value being -1.66 +/- 0.04. However, upon comparing the values from the Bright Quasar Survey at low redshift (z < 0.5) and high redshift QSOs detected by Chandra (z > 4), a slight steepening of alpha-ox is noted for the more distant objects. In most of the sources there is no significant requirement for a soft excess, although a weak thermal component (< 10% of Lx) cannot be excluded. There is an indication of spectral flattening (by delta gamma=0.2) at higher energies (> 3 keV, QSO rest frame) for the sample as a whole. This is consistent with the presence of a Compton reflection component in these radio-quiet AGN, with the scattering medium (such as an accretion disc or molecular torus) occupying a solid angle of 2 pi steradians to the X-ray source.

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arXiv2001

The highly variable X-ray spectrum of the luminous Seyfert 1 galaxy 1H 0419-577

An XMM-Newton observation of the luminous Seyfert 1 galaxy 1H 0419-577 is presented. We find that the spectrum is well fitted by a power law of canonical slope (gamma ~ 1.9) and 3 blackbody components (to model the strong soft excess). The XMM data are compared and contrasted with observations by ROSAT in 1992 and by ASCA and BeppoSAX in 1996. We find that the overall X-ray spectrum has changed substantially over the period, and suggest that the changes are driven by the soft X-ray component. When bright, as in our XMM-Newton observation, it appears that the enhanced soft flux cools the Comptonising corona, causing the 2-10 keV power law to assume a `typical' slope, in contrast to the unusually hard (`photon-starved') spectra observed by ASCA and BeppoSAX four years earlier.

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