Extragalactic Energetic Sources
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edited by V. K. KAPAH1 INDIAN ACADEMY OF SCIENCES BANGALORE Digitized by the Internet Archive in 2018 with funding from Public.Resource.Org https://archive.org/details/extragalacticeneOOunse Proceedings of the Winter School on Extragalactic Energetic Sources Organized by Tata Institute of Fundamental Research January 10-21, 1983, Bangalore Edited by V. K. Kapahi a supplement to Journal of Astrophysics and Astronomy The Indian Academy of Sciences Bangalore 560080 Acknowledgement for the cover picture Cover picture of 3C273 obtained with the MERLIN interferometer at 73 cm wavelength by R. G. Conway, R. J. Davis, A. Foley, T. Muxlow & T. Ray. MERLIN is owned and operated by Jodrell Bank, University of Manchester, England. Copyright © 1985 by The Indian Academy of Sciences, Bangalore 560080 Edited by V. K. Kapahi for The Indian Academy of Sciences, Bangalore 560080, typeset by Macmillan India Ltd., Bangalore 560025, and printed at Macmillan India Press, Madras 600041 Preface and acknowledgements The winter school on Extragalactic Energetic Sources was held at the Indian Institute of Science, Bangalore during January 10-21, 1983. The participants, numbering nearly a hundred, consisted largely of interested scientists and research students from various institutions and university groups in India, together with several experts from different parts of the world. The main purpose of the school was to provide an overview of the different aspects of powerful extragalactic sources and to highlight the recent developments, both theoretical and observational, that have taken place in this area. The principal speakers and the areas covered by them were: R. A. Laing (extended radio structures), M. H. Cohen (VLBI and compact radio sources), P. A. Strittmatter (optical and infrared studies), S. S. Murray & L. van Speybroeck (X-ray studies), M. J. Rees (models of active galactic nuclei) and G. R. Burbidge (non-cosmological nature of redshifts). In addition there were about a dozen seminars given by the participants. The present volume is a record of the proceedings of the winter school including some of the interesting discussions that took place following the various lectures. We note with regret that despite our best efforts we have been unable to include in the proceedings the contributions by Drs R. A. Laing, S. S. Murray and L. van Speybroeck. The school was organized by the Tata Institute of Fundamental Research with excellent support from the Raman Research Institute, Bangalore and the Indian Institute of Astrophysics, Bangalore. The facilities for holding lectures and housing the participants were kindly provided by the Indian Institute of Science, Bangalore. It is a pleasure to thank Professor J. V. Narlikar who shouldred most of the responsibility for the academic and administrative organization of the winter school. I am also grateful to a large number of colleagues who helped to make the school a success. I wish to thank The Indian Academy of Sciences for agreeing to publish the proceedings and Dr T. P. Prabhu and Ms Sandra Rajiva for providing invaluable editorial help. The radio photo of 3C 273 was very kindly made available by Dr R. G. Conway of Jodrell Bank. V. K. Kapahi TIFR Centre Bangalore ' Contents Preface and acknowledgements iii Inverse Compton X-rays and VLBI Radio Structures M. H. Cohen 1 Optical and Infrared Studies of Active Galactic Nuclei P. A. Strittmatter 13 Radio Sources and Galactic Nuclei: Models and Problems Martin J. Rees 53 Noncosmological Redshifts in Galaxies and Quasars G. R. Burbidge 87 Relativistic Motion in Quasars D. J. Saikia 105 3C 179 and Superluminal Source Statistics R. W. Porcas 113 Faraday Rotation and Magnetic Fields in QSO Absorption-Line Clouds P. P. Kronberg 119 Thick Accretion Discs—Luminosity Limits and Mass Outflow Rajaram Nityananda & Ramesh Narayan 127 Polarization Variability of Compact Extragalactic Radio Sources M. M. Komesaroff 133 Backward Emission in Quasars Jayant V. Narlikar 135 Gravitational Lensing and Quasars S. M. Chitre 143 Gravitational Lenses—The Multiple Scattering Limit Ramesh Narayan & Rajaram Nityananda 149 Mildly Active Nuclei of Galaxies T. P. Prabhu 155 M 82—A Nearby Laboratory for Rapid Star Formation and the Phenomena of Active Galactic Nuclei P. P. Kronberg 163 Nuclear Activity and Supernova Occurrence R. K. Kochhar 171 Other seminar talks not included in the proceedings 177 Participants 179 v ' ' Kapahi, V. K. (Ed.) Extragalactic Energetic Sources Indian Academy of Sciences, Bangalore, 1985, pp. 1-11 Inverse Compton X-rays and VLBI Radio Structures* M, H. Cohen Owens Valley Radio Observatory, California Institute of Technology, Pasadena, CA 91125, USA Contents 1. Introduction 1 2. Theory 2 3. Some Observations 5 3.1 NRAO140 5 3.2 3C345 6 3.3 3C84 (NGC1275) 6 3.4 Mrk 501 (1652 + 398) 6 3.5 3C147 7 3.6 1218 + 304, 2155-304 and 0548 -322 7 3.7 4C 39.25 (0923 + 392) 8 Appendix: Self-Compton X-rays 8 References 9 Discussion 10 1. Introduction The comparison of X-ray and VLBI radio data is particularly interesting and allows one, in some cases, to deduce that the emitting material is moving relativistically towards us. The analysis assumes that the radio radiation is incoherent synchrotron emission, so that the radio spectrum and angular size give the magnetic field strength and the energy spectrum of the relativistic electrons. The synchrotron photons collide with these same high-energy electrons, and X-rays are produced by the ‘self-Compton’ process. X-rays can also be produced by other mechanisms, of course, so the self- Compton calculation yields a lower limit to the X-rays. The calculation can first be made by assuming that the emitting material is at rest. In a few cases it is then found that the measured X-rays are many orders of magnitude weaker than the calculated lower limit, and the immediate conclusion is that the emitting material is moving towards us. Values of <5 (Doppler-shift factor) calculated this way are of order 10. In our discussion below, however, we will not be concerned with ratios of measured to expected X-rays, but will include 5 in the calculations from the beginning. * In his lecture. Professor Cohen also discussed the observational status of superluminal radio sources. For a more recent review on this subject the reader is referred to an article by M. H. Cohen & S. C. Unwin, in IA U Symp. 110: VLBI and Compact Radio Sources, Eds R. Fanti, K. I. Kellermann & G. Setti, D. Reidel, Dordrecht, p. 95.—Ed. 2 M. H. Cohen The utility of combining radio and X-ray data in this way was first emphasized by Burbidge, Jones & O’Dell (1974; hereafter BJO), and more recently by Marscher et al. (1979) and by Marscher & Broderick (198 la, b; 1982a, b). An important point made by BJO and by Marscher & Broderick (1981a) is that the calculation is distance- independent. Actually, the distance d comes into the calculation twice, via the depth of the source R = (pd. The optical depth is proportional to RN0, where N0 is electron density. But when N0 is estimated from the synchrotron turnover it is proportional to R~x, and d cancels. The redshift enters only in the ratio (1 + z)/<5 which controls the transformation of observables from one coordinate system to another. 2. Theory We assume that the source is a homogeneous sphere of angular diameter (p containing an isotropic power-law distribution of relativistic electrons N(E)dE — N0 E ~ p dE and a tangled magnetic field B. The sphere moves with Lorentz factor y = (1 -f}2)'112 at an angle 6 to the line of sight, giving a Doppler factor <5 = y_1(l -/?cos0)_1. Gould (1979) has calculated the radio and X-ray radiation from such a sphere. The spectrum is only a little different from the standard slab spectrum. A terrestrial observer measures the peak flux density Fm = F*[(l + z)/<5]“3 at frequency vm = vm[U + z)/<5] \ where the starred quantities are the peak values that would be measured by a co-moving observer. A schematic spectrum is shown in Fig. 1. The point (vn> ^n) is the intersection of the iow- and high-frequency asymptotes, and was used by BJO and Unwin et al. (1983); (vm, F'm) was used by Marscher et al. (1979), Simon et al. (1983) and others. We shall use (vm, Fm). For a homogeneous sphere these frequencies and flux densities are related by factors of order unity which are given in Table 1 in the appendix. At frequency v* the optical depth along the diameter of the sphere is 1.5. The cyclotron frequency and magnetic field can be calculated from ym, the Figure 1. Schematic spectrum of a compact source illustrating the definitions used in the text. Inverse Compton X-rays and VLB I radio structures 3 characteristic energy (in units of me2) of the electrons radiating at v*: eB _2/l + z\ (1) Vfi~2^~Vm7m V d ) and ym can be expressed in terms of the measured quantities Fm,vm, and </>. In practical units (Jy, GHz, milli-arcsec), ym = 103a(a)Fmvm2(/>“2 and B = \0~5b(a)Fm2v^(p4 Gauss, (3) where a (a) and b( a) are tabulated in the appendix. The b{a) used by Marscher (1983) is a little different because he used F'm rather than Fm. In Equations (2) and (3) B and ym are the magnetic flux density and electron energy in the source, and unstarred frequencies and flux densities are measured by the terrestrial observer. The angular diameter (/> is invariant in uniformly moving coordinate systems. The factor (\ + z)/b is readily understood in terms of the transformations between v and v*, and F and F*. Equations (2) and (3) are often used to calculate ym and B, and it has been customary to set 5=1.