Multi-Wavelength Observations of Galactic Black Hole X-Ray Transients
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UNIVERSITY OF SOUTHAMPTON Faculty of Physical Sciences and Engineering Department of Physics and Astronomy Multi-wavelength observations of Galactic black hole X-ray transients by Aarran Shaw A thesis submitted in partial fulfillment for the degree of Doctor of Philosophy October 2016 UNIVERSITY OF SOUTHAMPTON Abstract Faculty of Physical Sciences and Engineering Department of Physics and Astronomy Doctor of Philosophy Multi-wavelength observations of Galactic black hole X-ray transients by Aarran Shaw Galactic black hole X-ray transients (BHXRTs) represent the ideal opportunity to study accretion physics in extreme environments. Questions relating to accretion geometry, the mass of the compact object, how transient outbursts start and how jets form and evolve can only be answered by observing BHXRTs across multiple wavelengths. In this thesis I take a multi-wavelength approach to studying BHXRTs, and attempt to reconcile many aspects of accretion physics using a number of techniques. I have used timing analysis techniques to discover a super-orbital periodicity of 420 days in ∼ the X-ray and optical light curves of the BHXRT Swift J1753.5-0127, whilst also uncovering the likely orbital period of the candidate BHXRT MAXI J1305-704. X-ray spectral observations of Swift J1753.5-0127 revealed its first ever transition to a soft accretion state. This was found to be one of the lowest luminosity soft states ever recorded in such a system, at < 1% the Eddington luminosity, which proved crucial in the subsequent radio observations. Collaborators and I found that the compact jet had been quenched by a factor > 25, indicating that jet quenching was not dependent on accretion rate. In the optical regime, spectroscopy can reveal details about the mass of the compact object, which is important for population studies of black holes (BHs). I place a lower limit on the mass of Swift J1753.5-0127at M1 > 7:4 1:2M , confirming it as a BH and removing it from the so-called ± `mass gap.' However, optical observations can also reveal details about the accretion geometry of a source, as in the case of the BHXRT V404 Cyg, in which collaborators and I combined optical spectroscopy and photometry and found evidence for the 2015 outburst initiating 1 ∼ week before the X-ray outburst was detected. Our results were found to be consistent with the current disc instability model for transient outbursts. I summarise these findings and suggest avenues for future work in the closing pages of this thesis. Overall, this work shows that we can only truly understand BHXRTs once we have studied them across multiple wavelengths, and only in doing so can we discuss the underlying physics behind some of the most extreme regions of the Universe. Contents Abstract iii List of Figures ix List of Tables xi Declaration of Authorship xiii Acknowledgements xvi 1 Introduction 1 1.1 Basic Concepts . 1 1.1.1 Detecting X-rays . 1 1.1.1.1 Finding the location of X-ray sources . 3 1.1.2 Optical Astronomy . 4 1.1.3 Black Holes and Neutron Stars . 7 1.1.4 The Eddington Limit . 10 1.2 X-ray Binaries . 10 1.3 Low Mass X-ray Binaries . 12 1.3.1 X-ray transients . 16 1.3.2 The Spectrum of LMXBs . 18 1.3.3 X-ray spectral states and the Hardness Intensity Diagram . 21 1.3.3.1 Variability and timing analysis . 25 1.3.4 Determining compact object masses . 28 1.3.4.1 Measuring masses during outburst: The Bowen Fluores- cence Technique . 30 1.3.4.2 Distribution of masses: The Mass Gap? . 31 1.3.5 Observational differences between BH and NS LMXBs . 34 1.3.5.1 X-ray bursters . 34 1.3.5.2 NS LMXB states . 35 1.4 Swift J1753.5-0127 . 35 1.5 Thesis Outline . 37 2 A 420 day X-ray/optical modulation and extended X-ray dips in the short-period transient Swift J1753.5-0127 39 v Contents vi 2.1 Introduction . 39 2.2 Observations and Analysis . 40 2.2.1 Observations . 40 2.2.2 Light Curves . 40 2.2.3 X-ray dips . 41 2.3 Discussion . 44 2.3.1 The 420d modulation . 44 2.3.2 Properties of the 420d modulation . 46 2.3.3 Hard X-ray dips . 46 2.3.4 Comparison with other high-latitude X-ray transients . 47 2.4 Recent Developments . 49 2.5 Conclusions . 50 3 A low-luminosity soft state in the short period black hole X-ray binary Swift J1753.5-0127 51 3.1 Introduction . 51 3.2 Observations and Data Reduction . 52 3.2.1 Swift . 52 3.2.2 XMM-Newton . 53 3.2.3 NuSTAR . 55 3.3 Results . 56 3.3.1 The Light Curve and Hardness-Intensity Diagram . 56 3.3.2 Spectral Fits: Swift .......................... 57 3.3.3 Spectral fits: XMM-Newton and NuSTAR . 59 3.3.3.1 Disk blackbody plus power law . 59 3.3.3.2 Compton-upscattered disc blackbody . 59 3.3.3.3 Irradiated inner disc . 62 3.3.3.4 Investigation of reflection . 63 3.4 Discussion . 64 3.4.1 An unusual soft state . 64 3.4.2 The inner disc radius . 67 3.5 Conclusions . 68 4 Disc-Jet quenching of the Galactic black hole Swift J1753.5-0127 69 4.1 Introduction . 69 4.2 Observations and Data Reduction . 70 4.2.1 Archival radio observations (2005{2009) . 70 4.2.2 AMI-LA monitoring (2013{2015) . 71 4.2.3 JVLA observation (May 2015) . 71 4.2.4 Swift observations . 72 4.3 Results and Analysis . 75 4.3.1 10 year Radio and X-ray light curve . 75 ∼ 4.3.2 The X-ray / Radio Correlation of Swift J1753.5-0127 . 75 4.3.3 Soft-state quenching of the radio jet . 76 4.4 Discussion and Conclusions . 79 5 No evidence for a low-mass black hole in Swift J1753.5-0127 83 Contents vii 5.1 Introduction . 83 5.2 Observations and Analysis . 84 5.3 Results . 87 5.3.1 Companion star features . 88 5.3.2 Cross-correlation . 88 5.3.3 Disc emission lines . 89 5.3.3.1 Doppler Tomography . 91 5.4 Discussion . 94 5.4.1 Orbital Period . 94 5.4.2 Companion Star Features . 95 5.4.3 Mass of the primary . 98 5.5 Conclusions . 99 6 Testing the DIM: The 2015 outburst of V404 Cyg 101 6.1 Introduction . 101 6.2 Observations and Data Reduction . 103 6.2.1 Optical photometry . 103 6.2.2 Optical Spectroscopy . 103 6.3 Results . 104 6.3.1 Optical Photometry . 104 6.3.2 Optical Spectroscopy . 107 6.3.3 Spectral Energy Distribution (SED) . 109 6.4 Discussion and Conclusions . 110 7 On the orbital period of the Galactic transient MAXI J1305-704 113 7.1 Introduction . 113 7.2 Observations & Analysis . 114 7.2.1 X-ray observations . 114 7.2.2 Optical observations . 115 7.2.3 X-ray Light Curves . 115 7.2.4 Optical Spectroscopy . 119 7.3 Discussion . 122 7.3.1 The Orbital Period . 122 7.3.2 System Parameters . 122 7.4 Conclusions and Future Work . 123 8 Conclusions & Future Work 125 8.1 Future Work . 127 Bibliography 129 List of Figures 1.1 Illustration of the Chandra mirrors . 5 1.2 Schematic of a spectrograph . 6 1.3 Two-dimensional raw spectrum of V404 Cyg . 7 1.4 The innermost stable circular orbit . 9 1.5 Mass transfer in LMXBs and HMXBs . 12 1.6 The one-dimensional Roche potential . 13 1.7 The evolutionary path of an LMXB . 15 1.8 An artist's impression of a Low Mass X-ray Binary . 16 1.9 Schematic of a Be X-ray transient . 17 1.10 The hydrogen ionisation instability . ..