Observations of X-ray binaries using the Australia Telescope Compact Array-compact array ...

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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