-I 1 INFRARED INVESTIGATIONS OF GALACTIC•STRUCTURE AND THE X-RAY RAPID BURSTER by Anthony Wynn Jones BSc, ARCS Astronomy Group Blackett Laboratory Imperial College of Science and Technology London SW7 A thesis submitted for the degree of Doctor of Philosophy of the University of London and for the Diploma of Membership of the Imperial College May 1982 ABSTRACT INFRARED INVESTIGATIONS OF GALACTIC STRUCTURE AND THE X-RAY RAPID BURSTER A. W. Jones This thesis reports two astronomical projects made with the 1.5 m Tenerife telescope. First, a survey of near-infrared sources in the galactic plane, and second, the detection of bursts of infrared radiation from the X-ray source MXB 1730-335. The survey was made at 1.65 pm (H band) and 2.2 pm (K band) in 18 small areas on the galactic equator between longitudes 0° and 10°. It is complete to H = 10.5 and K = 9.5. This is equivalent to detecting type M giants at 6-7 kpc. Appendix A lists the equatorial coordinates and H and K magnitudes of 826 sources in a total area 2 of 0.18 deg . These sources account for 40-50% of the 2.4 pm surface brightness of the galactic disk. The observations are consistent with the presence of supergiants in the putative 5 kpc ring, but -2 are not conclusive. There is evidence for a population (~1000 deg ) of luminous, reddened objects, which may be supergiants within 0.4° (70 pc) of the galactic nucleus. Otherwise, the distribution of survey sources does not depend strongly on longitude. MXB 1730-335, the Rapid Burster, is inside the globular cluster Liller 1. It is unique in producing thousands of X-ray bursts a day in its active state. In 1979 two bright bursts of 2.2 pm radiation were detected from this object. They are notable for their 30 . great luminosity (10 W), accompanying flashes, and high brightness temperature (101G - 10"18 K) . Thf.se bursts are most plausibly associated with Type II X-ray bursts, although there were no simultaneous X-ray observations. A concerted international campaign failed to detect any further X-ray or infrared activity. Reports of radio bursts remain unsubstantiated. Appendix B contains papers written by the author on the Rapid Burster and on the statistics of supposed quasar-galaxy associations. 2 PREFACE The work reported in this thesis was carried out by the author in the Astronomy Group at Imperial College, under the supervision, of Dr M. J. Selby. It was part of a continuing collaboration between Imperial College and.Dr C. Sanchez Magro of the Instituto de Astrofisica de Canarias (IAC), La Laguna. Chapters 1 to 4 are an account of a survey of near-infrared sources in the galactic plane. The observational part of the project was conducted by the author in collaboration with M. Prieto Muhoz. The analysis and interpretation of the observations are by the author alone. Chapters 5 and 6 report the detection of bursts of infrared radiation from the X-ray source MXB 1730-335, the Rapid Burster. The observations which form the basis of Chapter 5 were obtained for the author by C. M. Mountain and C. Sanchez Magro. Subsequent monitoring of the source was conducted by the author in collaboration with C. Martinez Roger. All analysis, interpretation and criticism are by the author alone. Amendments in red are at the request of the Examiners. 3 ACKNOWLEDGEMENTS I thank first my supervisor, Mike Selby, for giving me free rein to pursue this work where I saw fit, and Professor Jim Ring for his wise counsel at several critical moments. Those who have worked at the Observatorio del Teide know well the frustrations, joys, miseries and triumphs of a long observing trip. I must thank my two colleagues at La Laguna who sat through it all with me. Mercedes Prieto assisted with the planning of the galactic plane survey and shared eight interminable weeks of scanning survey blocks and turning cryostats inside out. Carlos Martinez spent many chilly nights gazing at the rosy 2.2 pm glow from the inscrutable globular cluster that hides the Rapid Burster. We saw no bursts, but at least it got him his 'licenciatura'. Not so Mattias Mountain and Carlos Sanchez, who contrived to be in the right place at the right time to catch the elusive infrared bursts with 15 minutes to spare (and not many people have done that). Those observations spawned Chapters 5 and 6 of this thesis. For most of this time I was kept alive by a Research Studentship and a Research Assistantship from the Science and Engineering Research Council. I thank, too, Professor Francisco Sanchez for his generous support during a happy month in La Laguna and consequent forced learning of Spanish. Pat Kerridge typed this thesis to my somewhat precise specifications and still came out smiling. Finally, I wish to thank those friends and colleagues at Imperial College and La Laguna who have helped in innumerable ways during the course of this work. Above all I am grateful to Bob Joseph for his ideas, moral support and professionalism. 4 CONTENTS ABSTRACT 2 PREFACE 3 ACKNOWLEDGEMENTS 4 LIST OF TABLES 9 LIST OF FIGURES 10 CHAPTER 1 INVESTIGATION OF GALACTIC STRUCTURE BY INFRARED TECHNIQUES 12 1.1 Introduction 12 1.2 Surveys of diffuse 2.4 pm emission 15 1.2.1 The central bulge 17 1.2.2 The disk 18 1.2.3 Fine structure and dust 20 1.3 Surveys of discrete infrared sources 22 1.3.1 Two-Micron Sky Survey 22 1.3.2 AFGL Sky Survey 23 1.4 Consensus of the sky surveys 24 1.5 Objectives for a deep survey 25 1.6 Conclusions 26 CHAPTER 2 A SURVEY OF INFRARED SOURCES IN THE GALACTIC PLANE 27 2.1 Introduction 27 2.2 Survey area 29 2.3 Telescope and photometer 29 2.4 Doing the survey 33 2.4.1 Setting up 33 2.4.2 Calibration stars 34 2.4.3 Finding charts 37 2.4.4 Scan parameters 37 2.4.5 Scanning procedure 39 2.5 Outcome of the observations 41 5 CHAPTER 3 REDUCTION OF THE SURVEY DATA 43 3.1 The nature of the signal 43 3.1.1 The instrumental profile 43 3.1.2 Scans on the sky 45 3.2 Extracting the signal 45 3.2.1 Deconvolution 45 3.2.2 Correlation detection 46 3.3 Data reduction 49 3.3.1 Preparation of the raw data 49 3.3.2 Cross-correlation 51 3.3.3 Magnitude calibration 51 3.3.4 Detection of peaks 54 3.3.5 Refinement of source positions 57 3.3.6 Position calibration 57 3.3.7 Matching H and K sources 59 3.4 Presentation of the reduced data 59 CHAPTER 4 PRELIMINARY RESULTS FROM THE SURVEY 60 4.1 Introduction 60 4.2 Assessment of the survey results 64 4.2.1 Completeness 64 4.2.2 Limiting effects • 66 4.3 Surface number densities 68 4.4 Surface brightness 68 4.4.1 Distribution in longitude 70 4.4.2 Comparison with 2.4 jum observations 70 4.5 H-K colours 73 4.5.1 Contributions to H-K 73 4.5.2 Distribution of H-K colours 75 4.5.3 Supergiants near the galactic centre? 75 4.6 Block 1 and the galactic centre 76 4.6.1 Peculiarity of Block 1 76 4.6.2 Comparison with Becklin and Neugebauer's observations 77 4.7 Comparison with other catalogues 79 4.7.1 IRC -30321 / AFGL 2003 79 4.7.2 AFGL 2004 79 4.7.3 IRC -20416 81 4.7.4 IRC -20427 / AFGL 2062 81 6 4.8 Have we detected the 5 kpc ring? 81 4.9 Further work on optical identifications 82 4.10 Benefits of hindsight 83 4.10.1 The need for clear objectives 83 4.10 .2 Recommendations 84 4.11 Conclusions 85 CHAPTER 5 INFRARED BURSTS FROM THE X-RAY RAPID BURSTER 87 5.1 Characteristics of X-ray bursters 87 5.2 The Rapid Burster 89 5.3 Optical identification - Liller 1 90 5.4 Theoretical models 91 5.4.1 Thermonuclear flash 93 5.4.2 Accretion instability 93 5.5 The discovery of infrared bursts 94 5.6 Detection of infrared bursts at Tenerife 94 5.6.1 The observations 95 5.6.2 Calibration 95 5.7 Properties of the bursts 100 5.7.1 Luminosity and energy 100 5.7.2 Flashes 100 5.7.3 Brightness temperature 102 5.7.4 Comparison with X-ray bursts 103 5.7.5 Comparison with the Kavalur bursts 103 5.8 Coordinated observations of the Rapid Burster at several wavelengths 104 5.9 Infrared monitoring from Tenerife, Spring 1980 106 5.10 Results of the coordinated observations 106 5.11 Related infrared phenomena 108 5.11.1 Spurious phenomena 108 5.11.2 Questionable phenomena 110 5.11.3 Sky bursts 110 5.12 Conclusions 112 APPENDIX C CHAPTER 6 WHAT ARE THE INFRARED BURSTS? 114 6.1 Evidence for infrared bursts 114 6.1.1 Positive 114 6.1.2 Negative 114 6.2 Analysis of the evidence 115 7 6.3 Sources of energy 120 6.3.1 Garvitational energy 120 6.3.2 Nuclear energy 120 6.3.3 Implications for possible models 121 6.4 Reports of radio bursts 122 6.4.1 Assessment 122 6.4.2 Tests of origin 125 6.5 A speculative burst spectrum 126 6.6 What to do next 126 6.6.1 Problems of verification 127 6.6.2 Requirements for further observations 128 6.7 Conclusions 130 APPENDIX A A CATALOGUE OF INFRARED SOURCES IN THE GALACTIC PLANE 131 Blocks 1 and 2 132 Blocks 3 and 4 133 Blocks 16, 23 and 31 134 Blocks 32, 40 and 42 135 Blocks 52, 56 and 59 136 Blocks 62, 70 and 72 137 APPENDIX B PUBLICATIONS 138 IR flashes from the X-ray Rapid Burster 139 Quasars near companion galaxies: a reappraisal 141 REFERENCES 145 8 LIST OF TABLES 1.1 Near-infrared observations of the Milky Way with balloon-borne telescopes 16 1.2 Visibility of selected stars at 2.2 pm 26 2.1 Calibration stars used in the survey 35 2.2 Auxiliary data for scans 39 2.3 Observations of survey blocks 42 3.1 Calibration of survey blocks (H) 52 3.2 Calibration of survey blocks (K) 53 4.1 Analysis of source counts (H) 61 4.2 Analysis of source counts (K) 62 4.3 Longitudes, extents and areas of survey blocks 67 4.4 Comparison of survey sources with existing catalogues 80 5.1 Comparison of Type I and Type II X-ray bursts 90 5.2 Infrared observations of the Rapid Burster