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Compact Objects in Active Galactic Nuclei and X-Ray Binaries

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Compact Objects in Active Galactic Nuclei and X-Ray Binaries THE UNIVERSITY OF ST. ANDREWS Compact Objects in Active Galactic Nuclei and X-ray Binaries Edward M. Cackett Submitted for the degree of Ph.D. 4 August 2006 DECLARATION I, Edward Cackett, hereby certify that this thesis, which is approximately 50,000 words in length, has been written by me, that it is the record of work carried out by me and that it has not been submitted in any previous application for a higher degree. Date Signature of candidate I was admitted as a research student in October 2003 and as a candidate for the degree of Ph.D in October 2004; the higher study for which this is a record was carried out in the University of St Andrews between 2003 and 2006. Date Signature of candidate i In submitting this thesis to the University of St Andrews I understand that I am giving permission for it to be made available for use in accordance with the regulations of the University Library for the time being in force, subject to any copyright vested in the work not being a®ected thereby. I also understand that the title and abstract will be published, and that a copy of the work may be made and supplied to any bona ¯de library or research worker, that my thesis will be electronically accessible for personal or research use, and that the library has the right to migrate my thesis into new electronic forms as required to ensure continued access to the thesis. I have obtained any third-party copyright permissions that may be required in order to allow such access and migration. Date Signature of candidate I hereby certify that the candidate has ful¯lled the conditions of the Resolution and Reg- ulations appropriate for the degree of Ph.D in the University of St Andrews and that the candidate is quali¯ed to submit this thesis in application for that degree. Date Signature of supervisor ii Acknowledgements First, and foremost, I would like to thank my inspirational supervisors Keith Horne and Rudy Wijnands. Their enthusiasm, help, advice and insight (the list could easily continue) has been paramount to me enjoying astronomy research so much. The continual love and support of my parents and family throughout my educa- tion has always been much appreciated. Catr¶³ona, thank you for your love, support and friendship, it means the world to me. Thanks also to all my collaborators for insightful, and enjoyable discussions on many aspects of this work, especially Mike Goad, Kirk Korista, Hartmut Winkler, Craig Heinke and Dave Pooley. I would like to thank Sidney Harris (http://://www.sciencecartoonsplus.com), for kind permission to reprint his cartoons in this thesis. Finally, thanks have to go to all my o±ce mates who have put up with me over the years, but especially Nick and John - you were always there to provide distractions when I needed it (and even when I really didn't!). iii Preface This thesis is based on all the ¯rst author papers listed below. Additionally, Chapter 3 will shortly be submitted as a paper to MNRAS. [1] Cackett, E. M., Wijnands, R., Linares, M., Miller, J. M, Homan, J., Lewin, W. H. G. 2006, MNRAS, 372, 479 [2] Cackett, E. M, Wijnands, R. & Remillard, R. 2006, MNRAS, 369, 1965 [3] Cackett, E. M., Wijnands, R., Heinke, C. O., Edmonds, P. D., Lewin, W. H. G., Pooley, D., Grindlay, J. E., Jonker, P. G., Miller, J. M. 2006, MNRAS, 369, 407 [4] Cackett, E. M., Horne, K. 2006, MNRAS, 365, 1180 [5] Cackett, E. M., Wijnands, R., Heinke, C. O., Edmonds, P. D., Lewin, W. H. G., Pooley, D., Grindlay, J. E., Jonker, P. G., Miller, J. M. 2005, ApJ, 620, 922 iv THE UNIVERSITY OF ST. ANDREWS Compact Objects in Active Galactic Nuclei and X-ray Binaries Submitted for the degree of Ph.D. 4 August 2006 Edward M. Cackett ABSTRACT In this thesis I study the inner-most regions of Active Galactic Nuclei (AGN) us- ing the reverberation mapping technique, and neutron star low-mass X-ray binaries in quiescence using X-ray observations. Using the 13-year optical monitoring data for the AGN NGC 5548, the luminosity- dependence of the H¯ emitting radius was modelled using a delay map, ¯nding that the radius scales with luminosity as predicted by recent theoretical models. Time-delays between the continuum at di®erent wavelengths in AGN can be used to probe the accretion disc. Here, continuum time-delays in a sample of 14 AGN were used to measure the radial temperature pro¯le of the accretion discs, determine the nuclear extinction, and measure distances to the objects. However, the distances measured correspond to a value for Hubble's constant that is a factor of 2 lower than the accepted value. The implications of this on the thermal disc reprocessing» model are discussed. I present two Chandra observations of the neutron star transient in the globular cluster NGC 6440 in quiescence, where the power-law component to the spectrum is seen to be variable between the observations, suggesting that there is ongoing residual accretion. From a Chandra observation of the globular cluster Terzan 1, I have identi¯ed the likely quiescent counterpart to a transient previously observed in outburst, and discuss the other sources within the cluster. Using Chandra and XMM-Newton monitoring observations of two neutron star transients (KS 1731 260 and MXB 1659 29) in quiescence I have found that the neutron star crusts in both¡sources have now returned¡ to thermal equilibrium with the core. These observations also indicate that the crusts in both sources may have a high thermal conductivity and that enhanced neutrino emission may be occurring in the core. Finally, the discovery of an X-ray transient with XMM-Newton is presented, and the other sources in this observation discussed. v CONTENTS Declaration i Acknowledgements iii Preface iv Abstract v 1 Introduction 1 1.1 Active Galactic Nuclei . 3 1.1.1 Emission Lines . 4 1.1.2 Variability . 6 1.1.3 The current AGN paradigm . 6 1.2 Reverberation Mapping . 9 1.2.1 Time Delays . 10 1.2.2 Transfer Functions . 12 1.2.3 Techniques for analysing the variability . 12 1.3 Previous Observational Results . 14 1.3.1 Size and Radial Structure of the BLR . 14 1.3.2 Black Hole Masses . 15 vi 1.4 Continuum Variability . 16 1.4.1 Continuum reverberations and cosmology . 18 1.4.2 Alternative cosmological methods . 19 1.5 X-ray Binaries . 22 1.5.1 Transient Low-mass X-ray Binaries . 24 1.5.2 Neutron stars . 25 1.5.3 Neutron Star Formation in Low-Mass X-ray Binaries . 27 1.5.4 Low-Mass X-ray Binaries in Globular Clusters . 28 1.6 Quiescent Emission from Neutron Stars . 31 1.6.1 Quiescent Emission from Black Holes . 34 1.7 X-ray Astronomy . 35 1.7.1 Chandra X-ray Observatory . 37 1.7.2 XMM-Newton . 37 1.7.3 X-ray spectral analysis . 38 1.8 Thesis Outline . 39 2 Photoionized H¯ Emission in NGC 5548: it breathes! 41 2.1 Introduction . 41 2.2 Echo Mapping . 43 2.2.1 Luminosity-Dependent Delay Map . 44 2.2.2 Luminosity dependence of H¯ ux . 44 2.2.3 Luminosity dependence of time delay . 48 2.3 Parameterized models . 49 2.3.1 Static (S) . 51 vii 2.3.2 B1 . 52 2.3.3 B2 . 54 2.3.4 B3 . 55 2.3.5 B4 . 55 2.4 MEMECHO ¯t to the NGC 5548 AGN Watch 1989-2001 lightcurves . 57 2.5 Discussion . 60 2.6 Conclusion . 66 3 Testing thermal reprocessing in AGN accretion discs 68 3.1 Introduction . 68 3.2 AGN lightcurves . 70 3.3 Accretion disc model . 80 3.3.1 Disc Transfer Function . 82 3.3.2 Time-delays . 82 3.3.3 Applying this model to the Sergeev et al. data . 84 3.3.4 Extinction within the central regions of AGN . 85 3.4 Results . 88 3.4.1 The Hubble Constant . 95 3.5 Discussion . 95 3.5.1 Possible cosmological probe? . 102 3.6 Conclusions . 103 4 X-ray variability during the quiescent state of the neutron-star X-ray transient in the globular cluster NGC 6440 107 4.1 Introduction . 108 viii 4.2 Observations and Analysis . 109 4.2.1 Image Analysis . 109 4.2.2 Spectral Analysis . 111 4.3 Discussion . 117 5 A Chandra X-ray observation of the globular cluster Terzan 1 121 5.1 Introduction . 121 5.2 Observations and Analysis . 122 5.2.1 Source Detection . 123 5.2.2 Source Extraction . 129 5.2.3 Spectral Analysis . 130 5.3 Discussion . 136 5.3.1 The neutron-star X-ray transient X1732 304 in quiescence . 136 ¡ 5.3.2 Comparison with other globular clusters . 139 5.4 Conclusions . 140 6 Cooling of the quasi-persistent neutron star X-ray transients KS 1731 260 and ¡ MXB 1659 29 142 ¡ 6.1 Introduction . 142 6.1.1 KS 1731 260 . 143 ¡ 6.1.2 MXB 1659 29 . 145 ¡ 6.2 Observations and Analysis . 147 6.2.1 KS 1731 260 . 147 ¡ 6.2.2 MXB 1659 29 . 152 ¡ 6.3 Discussion . 155 ix 7 XMM-Newton Discovery of the X-ray Transient XMMU J181227.8 181234 in the ¡ Galactic Plane 163 7.1 Introduction . 163 7.2 XMM-Newton Observation . 164 7.3 Timing and Spectral Analysis . 165 7.4 RXTE All Sky Monitor observations . 169 7.5 Discussion . ..
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