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When referring to this work, full bibliographic details including the author, title, awarding institution and date of the thesis must be given e.g. AUTHOR (year of submission) "Full thesis title", University of Southampton, name of the University School or Department, PhD Thesis, pagination http://eprints.soton.ac.uk UNIVERSITY OF SOUTHAMPTON FACULTYOF PHYSICAL ANDAPPLIED SCIENCES PHYSICS AND ASTRONOMY Observations of X-ray binaries using the Australia Telescope Compact Array - Compact Array Broadband Backend by Daniel EmilioCalveloSantos Thesis forthe degree ofDoctorofPhilosophy July9, 2012 UNIVERSITY OFSOUTHAMPTON ABSTRACT FACULTYOF PHYSICAL ANDAPPLIED SCIENCES PHYSICS AND ASTRONOMY DoctorofPhilosophy OBSERVATIONS OFX-RAY BINARIES USING THE AUSTRALIAN TELESCOPE COMPACT ARRAY -COMPACT ARRAY BROADBAND BACKEND by DanielEmilioCalveloSantos The exploration of radio emission from the relativistic jets of X-ray binaries has becomekey tounderstandingaccretion ontocompactobjects. Upgrades toexisting radio telescopearrays haveimprovedtheabilityoftheseinstrumentsto detectfaint sources and theiruniquebehaviours. In thisthesis I address theuseof onesuch in- strument in observing several X-ray binary systems: the AustraliaTelescope Com- pact Array - Compact Array Broadband Backend (ATCA-CABB). Firstly, a study of the adverse effects that may arise when imaging spectrally variable sources us- ing broad bandwidths,with emphasison ATCA-CABB. Images are produced from model data and examined to find any false structures. I then discuss complications thatsuch features maycause whenattemptingto interpretreal structureinimages. Secondly, the results of attempts to observe the black hole X-ray binaries, GRO J1655-40andXTEJ1550-564,inquiescencewithATCA-CABBarepresented. Up- per limits from the non-detection of these sources are used in exploring the lower luminosityregion of the radio/X-ray correlation forhard state black hole X-ray bi- naries andtheimplicationsof“universal”scatterisdiscussed. Thirdly, a 16 day campaign observing the radio emission of the neutron star X- ray binary Circinus X-1 over a complete orbit during an historically faint state is presented. Variabilityinthesourceisexaminedandcorrectedimagesarecompared with archival maps in order to find any differences. I discuss my findings in terms ofsecularchanges injet geometryand behaviour. Finally, the first successful millimetre detections of neutron star X-ray binaries Circinus X-1 and Scorpius X-1 are presented. Sub-arcsecond jet structure in Circi- nus X-1 is compared to the existing centimetre maps, providing additional support fortheoriesproposedearlierinthethesis. Theradiotommspectrumofbothsources isestimatedand discussed. This thesis concludes with a description of the broader impacts of the above projects,as wellas possibilitiesforfutureresearch ineach field. C ONTENTS 1 Introduction 1 1.1 Abriefhistoryofradio astronomy . . . . . . . . . . . . . . . . . . 1 1.2 Radiointerferometry and aperturesynthesis . . . . . . . . . . . . . 5 1.2.1 Calibrationand deconvolution . . . . . . . . . . . . . . . . 9 1.3 TheAustraliaTelescopeCompact Array (ATCA) . . . . . . . . . . 13 1.3.1 TheCompactArray Broadband Backend (CABB) . . . . . . 14 1.3.2 MIRIAD . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 2 X-ray binaries and theirelectromagnetic emission 17 2.1 Emissionprocesses relevanttoXRBs . . . . . . . . . . . . . . . . . 17 2.1.1 Blackbody . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 2.1.2 Bremsstrahlung . . . . . . . . . . . . . . . . . . . . . . . . 18 2.1.3 Synchrotron . . . . . . . . . . . . . . . . . . . . . . . . . . 19 2.1.4 InverseComptonscattering . . . . . . . . . . . . . . . . . . 20 2.2 X-ray binaries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 2.2.1 Thecompactobject . . . . . . . . . . . . . . . . . . . . . . 22 2.2.2 Theaccretion disc . . . . . . . . . . . . . . . . . . . . . . . 24 2.2.3 Jets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 2.2.3.1 Formation . . . . . . . . . . . . . . . . . . . . . 28 2.2.3.2 Composition . . . . . . . . . . . . . . . . . . . . 30 2.2.3.3 Spectrum . . . . . . . . . . . . . . . . . . . . . . 31 2.2.3.4 Velocity . . . . . . . . . . . . . . . . . . . . . . . 32 2.2.3.5 Shocksand interactions . . . . . . . . . . . . . . 33 2.2.3.6 Precession . . . . . . . . . . . . . . . . . . . . . 36 2.2.3.7 Instabilities . . . . . . . . . . . . . . . . . . . . . 36 2.2.4 Thecorona . . . . . . . . . . . . . . . . . . . . . . . . . . 37 2.3 States,transitionsand multi-wavelengthcorrelations . . . . . . . . . 37 2.3.1 TheEddingtonlimit . . . . . . . . . . . . . . . . . . . . . . 37 2.3.2 Variableaccretion anddiscinstability . . . . . . . . . . . . 38 2.3.3 Black holeX-ray binaryoutburstsand states . . . . . . . . . 40 2.3.4 Thehardness-intensitytrack and aunified model . . . . . . 42 2.3.5 NeutronstarX-ray binary states . . . . . . . . . . . . . . . 45 iii iv Contents 2.3.6 Emissioncorrelations . . . . . . . . . . . . . . . . . . . . . 46 2.4 Thesisoverview . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 3 The effects ofvariablesource spectra onradio imaging 51 3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 3.1.1 Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 3.2 Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 3.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 3.3.1 Stablemodels . . . . . . . . . . . . . . . . . . . . . . . . . 58 3.3.2 Gradualmodels . . . . . . . . . . . . . . . . . . . . . . . . 59 3.3.3 Burstmodels . . . . . . . . . . . . . . . . . . . . . . . . . 62 3.3.4 Effectofsourcebrightness . . . . . . . . . . . . . . . . . . 62 3.4 A comparisonwithvariableflux densityartefacts . . . . . . . . . . 64 3.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 4 ObservationsofBHXRBs GROJ1655-40& XTE J1550-564 inquiescence 67 4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 4.1.1 GRO J1655-40 . . . . . . . . . . . . . . . . . . . . . . . . 69 4.1.2 XTEJ1550-564 . . . . . . . . . . . . . . . . . . . . . . . . 70 4.2 Observations& datareduction . . . . . . . . . . . . . . . . . . . . 70 4.2.1 GRO J1655-40 . . . . . . . . . . . . . . . . . . . . . . . . 71 4.2.1.1 Radio . . . . . . . . . . . . . . . . . . . . . . . . 71 4.2.1.2 X-ray . . . . . . . . . . . . . . . . . . . . . . . . 71 4.2.2 XTEJ1550-564 . . . . . . . . . . . . . . . . . . . . . . . . 71 4.2.2.1 Radio . . . . . . . . . . . . . . . . . . . . . . . . 71 4.2.2.2 Optical . . . . . . . . . . . . . . . . . . . . . . . 72 4.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 4.3.1 Fluxmeasurements . . . . . . . . . . . . . . . . . . . . . . 72 4.3.2 Correlations . . . . . . . . . . . . . . . . . . . . . . . . . . 74 4.3.3 Caveats . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 4.4 Discussionandconclusions . . . . . . . . . . . . . . . . . . . . . . 78 4.5 Addendum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 5 A completeorbit ofCircinus X-1 atanhistoricallyfaintepoch 81 5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 5.2 Circinus X-1 background . . . . . . . . . . . . . . . . . . . . . . . 82 5.3 Observations& datareduction . . . . . . . . . . . . . . . . . . . . 85 Contents v 5.3.1 Radio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86 5.4 Analysis& results . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 5.4.1 Flareevent . . . . . . . . . . . . . . . . . . . . . . . . . . 88 5.4.2 Imaging,modellingandsubtractions . . . . . . . . . . . . . 92 5.4.2.1 Originalimages . . . . . . . . . . . . . . . . . . 92 5.4.2.2 Differenceimages . . . . . . . . . . . . . . . . . 100 5.4.2.3 Modelsubtractedimages . . . . . . . . . . . . . . 103 5.4.3 Largescalestructure . . . . . . . . . . . . . . . . . . . . . 107 5.5 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 5.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 6 Millimetreobservations ofNSXRBs Circinus X-1 & Scorpius X-1 113 6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114 6.1.1 ScorpiusX-1 background . . . . . . . . . . . . . . . . . . . 115 6.2 Observations&datareduction . . . . . . . . . . . . . . . . . . . . 116 6.3 Analysis& results . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 6.3.1 CircinusX-1 . . . . . . . . . . . . . . . . . . . . . . . . . 119 6.3.1.1 Lightcurves . . . . . . . . . . . . . . . . . . . . 119 6.3.1.2 Spectrum . . . . . . . . . . . . . . . . . . . . . . 120 6.3.1.3 Imaging . . . . . . . . . . . . . . . . . . . . . . . 122 6.3.2 ScorpiusX-1 . . . . . . . . . . . . . . . . . . . . . . . . . 127 6.3.2.1 Lightcurves . . . . . . . . . . . . . . . . . . . . 127 6.3.2.2 Spectrum . . . . . . . . . . . . . . . . . . . . . . 130 6.3.2.3 Imaging . . . . . . . . . . . . . . . . . . . . . . . 132 6.4 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134 6.4.1 CircinusX-1’s varyingjet structure. . . . . . . . . . . . . . 134 6.4.2 NSXRB radioand mmspectrabehaviour . . . . . . . . . . 136 6.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 7 Conclusions & Future work 141 7.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141 7.2 Broaderconcepts &futureprospects . . . . . . . . . . . . . . . . . 143 7.2.1 Accountingfortheeffects ofvariableradio sources . . . . . 143 7.2.2 Continuedexplorationofradio/X-ray correlations . . . . . . 144 7.2.3 Thetwistedjets ofCircinus X-1 . . . . . . . . . . . . . . . 145 7.2.4 ThemmemissionofX-ray binaries . . . . . . . . . . . . . 146 7.3 Closingcomments . . . . . . . . . . . . . . . . . . . . . . . . . . . 148 vi Contents APPENDICES A VaSpecSim 153 B ExampleVaSpecSim response template 165 C VaSpecSim model parameters 167 Bibliography 175 LIST OF TABLES 3.1 Resultsofmodelrepetitionsusingdifferentsourceflux densities. . . 62 3.2 Resultsofvariableflux densitymodels . . . . . . . . . . . . . . . . 65 4.1 X-ray transientparameters, quiescentX-ray and radio fluxdensities 73 4.2 Best fitChandraspectraparameters forGRO J1655-40 . . . . . . . 76 4.3 OpticalResultsforXTE J1550-564 . . . . . . . . . . . . . . . . . . 76 5.1 CircinusX-1 observationlog . . . . . . . . . . . . . . . . . . . . . 87 6.1 CirX-1andScoX-1radiocmandmmobservationdetailsand mea- surements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 6.2 ComponentN flux measurements . . . . . . . . . . . . . . . . . . . 126 C.1 VaSpecSim modelparameters . . . . . . . . . . . . . . . . . . . . . 168 vii