Mullard Space Science Laboratory

A. J. Blustin
The nature and origins of warm absorbers in AGN

2004 (supervisor: G. Branduardi-Raymont)

This dissertation describes my analysis of XMM-Newton observations of six Active Galactic Nuclei (AGN), concentrating on the high resolution spectroscopy of soft X-ray absorption features, and discusses the results in the context of the origins and astrophysical implications of ionised outflows in AGN. I studied two Seyfert galaxies (NGC 3783 and NGC 7469) and four BL Lac objects (1H1219+301, H1426+428, Markarian 501 and PKS 0548-322), all of which have shown evidence in previous work of soft X-ray ionised absorption.

NGC 3783 has very deep soft X-ray absorption. I find that there are at least two main ionisation phases. The low ionisation phase appears to be fairly well concentrated around a single ionisation parameter, whilst the high ionisation phase probably contains a range of ionisation levels. NGC 7469 has a warm absorber with a much lower overall column in our line of sight. Despite this, the detected ions from its absorber span a range of four orders of magnitude in ionisation parameter. In the BL Lac objects, neither the RGS nor the EPIC spectra show any evidence of intrinsic ionised absorption. By looking back over the history of observations of ionised X-ray absorption in these sources, I am able to show that the existence of such features can be ruled out at 93 percent confidence.

I compare the results of these analyses with findings from high resolution X-ray spectroscopic observations of other AGN, in order to come to some conclusions about the origins and importance of the warm absorber phenomenon. I find that Seyfert, NLSy1 and certain QSO absorbers are most consistent with an origin in the dusty torus, whilst the outflows in two QSOs are more likely to be accretion disc winds. I show that the kinetic luminosities of the torus outflows must account for less than 1 percent of the bolometric luminosities of the AGN.


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