\I ASA SP-453 GAMMA RAY ASTROPHYSICS New Insight into the Universe NASA SP-453 GAMMA RAY ASTROPHYSICS New Insight into the Universe Carl E. Fichtel and Jacob I. Trombka NASA Goddard Space Flight Center Scientific and Technical Information Branch 1981 NASA National Aeronautics and Space Administration Washington, DC For sale by the Superintendent of Documents U.S. Government Printing Office, Washington, D.C. 20402 Library of Congress Catalog Card Number 81-600116 Foreword Our aim in writing this book on the new field of y-ray astronomy is to provide a text which describes the astrophysical significance of these highest energy celestial photons, and to assemble in one place a treatment on y-rays emitted from bodies in the solar sys- tem, from within our galaxy, and from beyond our galaxy. The special importance of y-ray astronomy has long been realized by astronomers and physicists, and theorists have pursued many aspects of this field in some detail. Hence, it is possible to de- scribe the significance of several problems in y-ray astrophysics and discuss the potential implications of anticipated results, as well as existing ones. Gamma ray astronomy has already yielded several sur- prises, including y-ray bursts of unknown origin and intense pulsed y-radiation from radio pulsars. Not only was the strong pulsed radiation a surprise, but in at least one case the phase is quite different from that in the radio range. Further there are observed y-ray emitting objects for which the originatingmechan- ism can only be determined with certainty after improved measurements are made. This book is intended for those in astrophysics who wish to have the opportunity to learn more about the evolving field of y-ray astronomy and its relationship to the high energy, evolu- tionary processes occurring in the universe. We have assumed that the readers will have had basic undergraduate courses in physics, including electromagnetic, atomic, and nuclear theory, and will be familiar with the rudiments of astronomy. We have attempted to write those portions where reference to the content of more advanced astronomy and physics courses is appropriate in such a way that the general flow of thought will not be inter- rupted in a significant way for readers unfamiliar with the details of the particular theories involved, yet those with a full under- standing of the theories will see the validity and qualifications clearly. We considered whether to discuss the y-ray production and interaction processes together near the beginning of the book or to describe each as it occurred in a development built around astrophysical subjects. After considerable thought and the exper- ience of teaching courses in X-ray and y-ray astrophysics and planetary physics, the latter approach was chosen. This decision resulted partially from the natural development of the theory in terms of specific applications, partially from the assumption that the readers have already had the basic physics and astronomy background, and partially from what appears to be the students enthusiasm and our own for studying the astrophysical phenom- ena under consideration and, therefore, allowing the needed sup- porting calculations to be derived or introduced as they are re- quired. We have left to the end of the book a general discussion of the experimental aspects of the field which, for the most part, seem best treated together, separately from the development of the astrophysical aspects of y-ray astronomy. The present time seems to be particularly appropriate for a new book on y-ray astrophysics in view of the existing pause between the satellite and other experiments of the 1970's whose results have formed the foundation for this field and the major advances that should occur in the late 1980's. Also, as noted earlier, the relevant theoretical work is at hand so that meaning- ful discussions of the results and future expectations are possible. This book would not have been possible without the coop- eration of a large number of individuals. We gratefully acknow- ledge the use of information supplied to us by several scientists before it appeared in the open literature. We would especially like to acknowledge the following individuals for their help: C. Andre of the Smithsonian Institution; J. Arnold of the Uni- versity of California, San Diego; E. Chupp of the University of New Hampshire; J. Lapides of the National Institutes of Health; A. Metzger of the Jet Propulsion Laboratory; R. Reedy of the Los Alamos Scientific Laboratory; G. Steigman of the Bart01 Research Foundation; and T. Weekes of the Mount Hopkins Observatory; A. Opp of NASA Headquarters; D. Bertsch, C. Crannell, R. Hartman, D. Kniffen, J. O'Keefe, D. Thompson; and L. Yin of the Goddard Space Flight Center; for their supplying special materials or critically reviewing the text; R. Tanner of the Goddard Space Flight Center and Eileen Sapcariu of the Systems and Applied Sciences Corporation for their valuable efforts in scientific editing; Elaine Brown, Candy Clark, Rose Ramberg, Teri Wernick, and especially Jaci Mills for their patience and good humor in typing the manuscript; David Okamoto and John Mathes for preparing a number of the graphs and patiently reviewing the nuclear tables. Our special thanks are given to J. Brandt and F. McDonald of the Goddard Space Flight Center and A. Opp and W. Quaide for their interest and support of this work. We wish also to thank Elsie Trombka for her cheerfulness and help over this trying period of our writing this book. Contents Chapter PART I .INTRODUCTION 1 GAMMA RAY ASTRONOMY IN PERSPECTIVE ... 3 PART I1 .THE SOLAR SYSTEM 2 GAMMA RAY OBSERVATIONS OF THE SOLAR SYSTEM ............................ 19 Introduction ............................. 19 Models of Solar System Evolution ............. 20 Solar System Gamma Ray Astronomical Observations ............................. 21 3 PLANETS. COMETS. AND ASTEROIDS .......... 25 Introduction ............................. 25 Interaction Processes ....................... 26 Primary and Secondary Galactic Cosmic Ray Interactions .......................... 33 Experimental Results ...................... 49 4 SOLAR OBSERVATIONS ..................... 67 Introduction ............................. 67 Interaction Processes ....................... 68 Experimental Results ...................... 86 Chapter PART 111 .THE GALAXY 5 THE INTERSTELLAR MEDIUM AND GALACTIC STRUCTURE ..................... 99 Introduction ............................. 99 Interaction Processes ....................... 99 Galactic Matter Distribution ................. 107 Galactic Cosmic Ray Distribution ............. 110 Current Gamma Ray Results and Their Interpretation ....................... 113 6 COMPACT OBJECTS ......................... 131 Neutron Stars and Pulsars ................... 132 Supernovae .............................. 140 Black Holes .............................. 143 Other High Energy Gamma Ray Sources ........ 146 Low Energy Gamma Ray Bursts .............. 148 PART IV .EXTRAGALACTIC RADIATION 7 GALAXIES ................................. 165 Normal Galaxies .......................... 165 Introduction to Active Galaxies .............. 168 Seyfert Galaxies .......................... 171 Radio Galaxies ....... ................... 173 Quasars ................................. 174 BL Lacertae Objects ....................... 178 Concluding Remarks ....................... 180 8 COSMOLOGY ............................... 187 Introduction ............................. 187 Diffuse Radiation ......................... 189 Chapter TheValue~ofH~andqo ................... 195 Matter-Antimatter Symmetry or Asymmetry .............................. 197 9 DIFFUSE RADIATION ....................... 203 Introduction ............................. 203 Observations ............................. 203 Possible Contributors to the Diffuse Radiation ............................... 208 Summary ................................ 219 PART V .INSTRUMENTATION 10 GAMMA RAY INTERACTION PROCESSES ....... 229 Introduction ............................. 229 Photoelectric Effect and Fluorescence Radiation ............................... 232 Pair Production and Annihilation Radiation ............................... 233 Compton Scattering ....................... 242 Electron Leakage and Bremsstrahlung .......... 244 11 DETECTORS FOR ENERGIES LESS THANlOMeV .............................. 247 Introduction ............................. 247 Properties of Detectors ..................... 248 Detector Response to Monoenergetic Radiation ............................... 264 Detector Efficiency ........................ 274 Detector Flight Systems .................... 287 Chapter 12 DETECTORS FOR ENERGIES GREATER THAN 10 MeV .............................. 305 Introduction and History ................... 305 The High Energy Gamma Ray Interaction ....... 312 Experimental Approach .................... 315 Angular Resolution ........................ 324 Energy Resolution ......................... 329 Instrument Performance and Data Analysis ................................. 331 13 ANALYSIS OF OBSERVATIONAL SPECTRA ..... 337 Introduction ............................. 337 General Formulation ....................... 337 Calculation of Errors ....................... 341 Methods of Solution ....................... 344 Compensation for Gain Shift and Zero Drift ............................... 346 Analysis of Mixture of Discrete Lines and Continuum ...................... 349 Analysis of High Energy Resolution Discrete Line Spectra