Three-fifths of five-eighths of bugger-all
Philip Edwards
ISAS, Sagamihara, Kanagawa, Japan
abstract
The research career of Dave Jauncey is reviewed and some trends identified. Dave’s
contributions amount to significantly more than the title of this article, which is one
of the more colourful expressions Dave occasionally uses.
1
Introduction
When preparing this presentation I found, to my surprise, that ADS included papers from
International Cosmic Ray Conference proceedings from the early 1960’s, and so it seemed that
this year marked the 40th anniversary of Dave Jauncey’s first scientific publication, which
appeared in the proceedings of the the 8th International Cosmic Ray Conference (ICRC), held
in Jaipur, India. In fact, (and I am indebted to Roger Clay for setting the record straight)
Dave is a co-author on a paper from the preceding
√ ICRC, which was held in Kyoto in 1961.
So, to be more precise, this year marks the (40 ± 40)th anniversary of Dave’s first paper...
Dave did his PhD with the cosmic ray group of the University of Sydney, and this paper
will examine Dave’s research career starting with period. The question of why Dave left cosmic
ray studies for radio astronomy is a natural one to ask, but I will endeavour to show that the
more relevant question is in fact whether Dave has ever left cosmic ray research!
2
Cosmic Rays
The cosmic ray flux consists principally of fully ionized atomic nuclei. The steeply falling energy
spectrum extends from below 1010 eV to above 1020 eV. The energy density of the cosmic rays
at the earth is ∼0.5 eV cm−3 , roughly the same as that of the Galactic magnetic field, starlight,
and the average kinetic energy density of gas clouds, and a factor of two higher than that of
the cosmic microwave background (e.g., Erlykin & Wolfendale, 2001).
Cosmic rays have been extensively studied since their discovery in the early 1900s. (The
closely related, if more amusing, field of comic rays has developed unhindered by the increasing
sophistication of spell-checkers, and is also the topic of active research [e.g. Medina-Tanco,
1998].)
Cosmic ray particles interact with atmospheric nuclei, resulting in the production of secondary particles, which will in turn interact. At energies above 1014 eV, these cascades, or air
showers, may survive to sea-level, where they can be studied by air shower arrays.
In the early 1960s the University of Sydney’s cosmic ray group was studying the nucleonic
and electromagnetic structure of cosmic ray air showers. The group’s contributions to the Jaipur
International Cosmic Ray Conference, including some of Dave’s first papers, were presented at
the meeting by Prof. McCusker. The questions and answers following the presentation are
recorded in the proceedings, and it is notable that among those asking questions were M. Oda
(who later became the father of Japanese X-ray astronomy) and M. Koshiba (who shared the
2002 Nobel Prize in Physics).
One of the questions concerned the differences between “flat core-structure” and “steep
cores”, terms also applicable to the spectral study of AGN, a first indication that the fields of
PeV cosmic rays and µeV radio astronomy are not as far removed as they might appear. This
impression is reinforced by Figure 7 of McCusker’s paper (reproduced in Figure 1). The lower
plot could readily pass for a radio-astronomical image. It turns out that this is a simulated
cosmic ray event, intended to reproduce the observed particle distribution shown in the upper
figure (the same radio image with a dirtier beam). The simulation was carried out on the
silliac, a machine I profess to having been woefully ignorant about, but which I am now in a
position to state did not, as it might appear, derive its name from ‘Silly Acronym.’
2.1
SILLIAC
silliac actually stands for the Sydney version of the Illinois Automatic Computer. The illiac
was built by the University of Illinois in the early 1950s, based on the Princeton Institute for
Advanced Study architecture developed by John von Neumann. illiac contained 2800 valves
and 20 km of wire with 54000 connections, with a total weight of five tons, but its success
accelerated the computing revolution:
“At the University of Illinois, illiac I, as it became known, was used campuswide,
and its success spread the computer philosophy to other campuses. In 1955–56, it
was copied by Michigan State University as the mistic and also by the University
of Sydney, Australia, where it was bravely named the silliac. Later, one was
constructed by Iowa State University as the cyclone.”
— http://www.ece.uiuc.edu/pubs/centhist/five/DCL1.HTM
The silliac was constructed in the mid 1950s, and was in operation until 1968. The
illiac played an important role in the development of computer music (e.g., http://cmprs.music.uiuc.edu/history/illiac.html), and the silliac was put to similar use:
“I must confess I don’t remember very much about it except that all the programming was done on punched paper tape and that they had one program which would
play ‘Waltzing Matilda’ through the loudspeaker of the computer, doubling the
speed on each repetition.”
— http://neuron.tuke.sk/∼hudecm/txt/Talking%20nets%20-%20Arbib.txt
In the light of Carl Gwinn’s proposal at this meeting to fund research via the purchase
of lottery tickets, it is of interest to note that the silliac, “was funded partly by Melbourne
Cup winnings of £50,000 from one of the University’s benefactors, Adolph Basser, in the early
1950s.”
The same article quotes Emeritus Professor John Bennett, Founding Professor of Computer
Science, recalling that
“One useful point of the silliac design was a feature of the cooling facility, which
used a refrigerated heat exchanger to cool the circulating air. Each of these units
was just the right size to hold half a dozen bottles of beer. Very useful.”
– http://www.usyd.edu.au/publications/news/010810News/1008 computer.html
Clearly computer scientists also share a thirst for more than just the pursuit of knowledge!
Figure 1: Observed (top) and simulated (bottom) plots of number density of a cosmic ray event
(from McCusker 1963).
Figure 2: The title and author list for one of the Sydney contributions to the 8th International
Cosmic Ray Conference in Jaipur, 1963.
3
Leaving Cosmic Rays
So why did Dave (appear to) leave cosmic ray studies? One possible reason lies in the fact
that the cosmic ray energy spectrum falls steeply: the differential spectrum has an index of
almost −3. Thus the cosmic ray flux, which is of the order of 1 particle per m2 per second
near 1010 eV, falls to 1 particle per m2 per year near 1015 eV, and 1 particle per km2 per year
around 1018 eV (see, e.g., Cronin 1999). As the cosmic ray group’s interests were shifting to
these higher energies (resulting in the construction of SUGAR — the Sydney University Giant
Air-shower Recorder — near Narrabri in the late 1960s), it would have become clear to Dave
that the fluxes to be investigated would be approaching the order of 1 particle per km2 per
PhD-student-candidature. Radio astronomy may well have appeared as a greener pasture.
However, another reason for the shift in Dave’s interests may be found in Figure 2. The moral
of the story is clear: if you want your good students to continue, then at the very least be sure
to spell their name correctly!
4
Radio Astronomy
As it turned out, Dave’s familiarity with steeply falling spectra had immediate application to
radio astronomy, particularly in the interpretation of log N – log S plots: “Re-examination of
the Source Counts for the 3C Revised Catalogue”, Jauncey (1967), “Some Comments on a
Paper ‘Least-Squares Fit of a Gaussian to Radio Sources’ by S. Von Hoerner”, Jauncey (1968),
“Maximum-Likelihood Estimation of the Slope from Number-Flux Counts of Radio Sources”,
Crawford, Jauncey & Murdoch, (1970), and “Radio surveys and source counts”, Jauncey (1975).
Those wishing to use integral counts in their analysis have been warned!
5
Pulsars
Some of Dave’s early radio astronomical work was carried out at Arecibo. This was the late
1960s and coincided with the discovery of pulsars. The authoritative account of the origin of
the name pulsar might be expected to come from their discoverer:
“The name ‘pulsar,’ by which they are now known, was not coined by us but by
a journalist. It was found written on the blackboard in one of our offices and
responsibility has been claimed by the science correspondent of the Daily Telegraph.”
— J. Bell Burnell in “Serendipitous Discoveries in Radio Astronmomy”
However, there exists a counter-claim:
“Meanwhile, I’d gotten tired of trying to get my mouth around the term ‘rapidly
pulsating radio sources.’ In a paper I wrote for Science with two of my graduate
students, Hal Craft and John Comella, I coined a shorthand term — “pulsars” —
and the name stuck. We could now talk about them with ease, even as we struggled
to determine what they were.”
— F. Drake (with D. Sobel) “Is Anyone Out There?”
Tracking down the paper in Science (Drake et al. 1968), one discovers that the credit in
naming is shared a little more evenly (“...we, along with others, have come to call the objects
‘pulsars’.”), and that the paper has three other co-authors, one of whom is none other than
Dave. A (non-exhaustive) search of the literature does suggest that this is the first use of the
word “pulsar” in a refereed scientific journal.
Dave’s work on pulsars did not stop with the observations of CP 1919 reported in this paper,
continuing with observations of the Vela pulsar — “Size of the Vela Pulsar’s Radio Emission
Region: 500 Kilometers” (Gwinn et al. 1997) “Size Of the Vela Pulsar’s Emission Region at 13
Centimeter Wavelength” (Gwinn et al. 2000a), “Observations of the Vela Pulsar Using VSOP”
(Gwinn et al 2000b).
The reason for this (perhaps surprising) interest in pulsars becomes clear when it is realised
that pulsars have been proposed as a possible source for cosmic rays with energies above the
so-called ‘knee’ in the cosmic ray spectrum at ∼ 1015 eV:
“There is even more discussion about the nature of the sources here. A ‘special’
variety of SN (which we denote as SSNR - i.e. super-supernovae) and/or pulsars
seems likely.
“Turning to pulsars, the inevitable uncertainties in the environment of these highly
condensed objects means that the acceleration mechanism is uncertain. However,
it is apparent from general arguments that a millisecond pulsar should be able to
accelerate iron nuclei to 1020 eV. The time interval just after the birth of the pulsar
when such energetic particles are produced will be very short but it will extend as
the energy falls.”
— Erlykin & Wolfendale, 2001
6
Origin of the highest energy CRs
It is widely accepted that galactic sources, particularly supernovae, are responsible for the
production of cosmic rays up to energies near the knee in the spectrum. At the highest energies,
however, the rigidity of particles is so high that they are not trapped in the galaxy’s magnetic
field. Assuming that cosmic rays at these energies are accelerated (and not directly produced
with these energies by some more exotic phenomenon), constraints can be placed on the product
of the size and magnetic field of the accelerating region (e.g., Hillas 1984, Cronin 1999). Radio
galaxy lobes and AGN are both potential sites for the acceleration of the highest energy cosmic
rays, however, with the discovery of the cosmic microwave background came the realisation that
it would impose a cutoff in the spectrum of the highest energy cosmic rays. The cutoff, now
know as the Greisen–Zatsepin–Kuz’min (or GZK) cutoff, effectively limits the sources of cosmic
rays with energies above 1020 eV to distances within several hundred Mpc. The detection of
a cosmic ray with an energy of 3×1020 eV led to a detailed consideration of its possible origin
(Elbert & Sommers 1995). “Obvious” candidate local sources, such as Cen A and M 87, would
require larger than expected inter-galactic magnetic fields to bend the particle’s trajectory
sufficiently. Elbert & Sommers noted that the bright AGN 3C 147 lies in the nominal error
box for the arrival direction of the event, although some non-standard physics or non-standard
neutral particle would need to be postulated as, at z = 0.545, has an a luminosity distance of
3100 Mpc.
That has not stopped the coincidence from being seized upon by theoreticians, with Farrar
& Biermann (1998) claiming that the five highest energy cosmic ray events are all aligned with
compact radio-loud quasars. (The criticisms of Hoffman [1999] of this work were addressed in
the reply of Farrar & Biermann [1999].) More recently, it has been proposed that M 87 may be
the source of all the highest energy cosmic rays (Ahn et al. 2000). A large international project,
the Pierre Auger Observatory, is being constructed in an attempt to determine (among other
things) the origin of the highest energy cosmic rays (http://www.auger.org/).
It should come as no surprise to find that all these postulated sources of the highest energy
cosmic rays have already been examined by Dave: e.g., M87 (Cohen et al. 1969; Kellermann et
al. 1973; Morabito et al. 1988), 3C 147 (Clark et al. 1968; Kellermann et al. 1971; Preston et
al. 1985), Cen A (Jauncey et al. 1995; Tingay et al. 1998; Tingay, this meeting).
Inspection of the author lists of these papers reveals another theme of Dave’s research career:
that of the importance of collaborations.
7
Collaborations
Collaborations are becoming increasingly important in research. Possibly most prolific collaborator to date was mathematician Paul Erdös (1913–1996). There is a website dedicated to
detailing his collaborations (http://www.oakland.edu/∼grossman/erdoshp.html), entitled The
Erdös Number Project. By way of introduction, the website reproduces an article from the
Economist, which notes Erdös
“...had no children, no wife, no house, no credit card, no job, no change of shoes,
indeed nothing but a suitcase containing a few clothes and some notebooks. Neither
was he fussy about food, as long as he had coffee. A mathematician, he said, ‘is a
machine for converting coffee into theorems’.”
Erdös’s collaborations have been studied by examining the American Mathematical Society’s
Mathematical Reviews database. At the time of the last review, there were about 1.6 million
Figure 3: The distribution of number of authors on Dave’s papers. The tail of the distribution
is considered further in Figure 4.
authored items in the database, by a total of about 337,000 different authors. Approximately
66% of these items were by a single author, 26% by two authors, 7% by three authors, and 1%
by four authors. The fraction of items authored by just one person has steadily decreased over
time, starting out above 90% in the 1940s and currently hovering just under 50%.
Erdös published 1401 papers, and coauthored papers with 502 people (although papers he
has contributed to continue to appear). In order to study the nature of collaborations and the
interconnectivity of researchers, people with whom Erdös has coauthored a paper are assigned
an Erdös number of 1. Those who have not coauthored a paper with Erdös, but who have
coathoured a paper with one of Erdös’s collaborators, are assigned an Erdös number of 2, etc.
Albert Einstein has an Erdös number of 2, as both he and Erdös coauthored papers with
Ernst Straus (in Einstein’s case, “The Influence of the Expansion of Space on the Gravitation
Fields Surrounding the Individual Stars” [Einstein & Straus 1945]). Bill Gates has an Erdös
number of at most 4.
The distribution of finite Erdös numbers has a median of 5, a mean of 4.69, and a standard
deviation of 1.27. The highest finite Erdös number is 15. In addition, there are about 45,000
mathematicians who have collaborated but who have an infinite Erdös number, and 84,000
who have never published joint works. Since Erdös collaborated with so many people, this
distribution is shifted downward from that of a random mathematician.
The NASA Abstract Data Service (http://adswww.harvard.edu) provides an amenable
means of studying Dave’s collaborations (although it is apparent that the ADS is, or was
at the time of writing, incomplete in some areas in the 1960s). At the time of writing there
were 200 refereed papers of Dave’s listed in the ADS database. The distribution of the number
of authors on a paper is shown in Figure 3. The distribution has a mode of 4, and a median
Figure 4: The number of authors on Dave’s papers in (quasi-) chronological order. The large
spikes are, in turn, (paper no. 94) multi-wavelength observations of the rapid burster (Lawrence
et al. 1983), the first TDRSS and SHEVE papers clustered around paper no. 120, the TDRSS
15 GHz paper at paper no. 131, the VSOP paper in Science (no. 148) and the VSOP overview
and VSOP Survey Program papers in PASJ in the 180’s.
of 6, with an appreciable tail. It is interesting to look at the distribution as a function of time,
as shown in Figure 4, where the paper number treats all 200 papers in (quasi-)chronological
order (as no attempt is made to order papers published in the same year). A general trend for
larger collaborations with time is apparent.
Dave has published papers in refereed journals with (at least) 480 collaborators, not far behind Erdös! This naturally suggested the possibility of generating “Jauncey numbers,” however
it quickly became apparent that, as almost all participants at the conference have collaborated
with Dave at some time, nearly everyone has a Jauncey number of 1.
An alternative would be to start from the father of radio-astronomy and assign “Jansky
numbers”. This immediately encounters the problem that Jansky does not appear to have
coauthored papers with anyone. Everyone has an infinite Jansky number! A compromise
would be to instead determine the “Reber number” for radio astronomers. Although perhaps
not renowned for his collaborative work, Reber nevertheless coauthored papers with ∼20 people (see, e.g., http://www.gb.nrao.edu/∼fghigo/fgdocs/reber/greberref.html). It appears that
Dave Jauncey has a Reber number of 3. Reber collaborated with G.R.A. “Bill” Ellis, who thus
has a Reber number of 1. Ellis collaborated with Peter McCulloch, who has a Reber number
of 2, and Dave has coauthored a number of papers with Peter.
And, putting things back into their proper perspective, we can conclude that Grote Reber
has a Jauncey number of 3.
8
Space VLBI
As illustrated in Figure 4, Dave has been involved in Space VLBI from the TDRSS days. As a
member, and more recently co-chair, of the VSOP International Science Council (VISC), Dave
has been a tireless supporter of efforts to obtain the longest possible baselines for VLBI. (One
effort to commemorate this was made in VSOP News no. 72, from September 1997:
During the Kyoto IAU General Assembly in August, ‘The Sidereal Times’ was published daily with a variety of serious reports as well as some more light-hearted
information from Seth Shostak and his co-editors. Following their lead, we note
that in science we use units which in many cases originate from physicists’ names,
with the majority of physicists thus honored being from the northern hemisphere.
One of VISC resolutions in Kyoto was to use the ‘Jauncey’ instead of ‘Jansky’ for
measuring the flux density of southern hemisphere sources. Brightness temperatures
will still be expressed in Kelvin, though for southern sources this will honour Kelvin
Wellington!
— http://www.vsop.isas.jaxa.jp/obs/news/www.72.html
The inimitable sense of humour of VSOP Project Scientist “Hirax” Hirabayashi is evident.)
Dave has always been concerned with HALCA’s expected lifetime. Before launch, it was
thought that degradation of the solar panels would be a key factor in determining how long
HALCA could operate. A steady decline, superimposed on the annual seasonal cycle, is evident
in the power generated by the solar panels (e.g., Murata 2000), although it is not a severe as
the original (conservative) predictions. While concern for HALCA’s lifetime is quite natural,
perhaps it is only Dave who can view the diminishing power supply as an interesting measure
of the net exposure of the solar panels to the cosmic ray flux!
9
Intra-Day Variability
The most recent area of research to which Dave has made significant contributions is in the
study of Intra-Day Variability (see, e.g., the contributions of Bignall, Kedziora-Chudczer, Lovell,
Macquart to this meeting). (Indeed, as between them Dave Heeschen (1982, 1984) and Dave
Jauncey (and their respective colleagues) have made such large contributions to this field one
might suspect IDV stood for Intra-Dave Variability...)
As one might by now expect, there is once again a cosmic ray connection with these studies
(and I am grateful to Joseph Lazio for drawing my attention to it during his presentation at
meeting celebrating the 10th anniversary of the VLBA in Socorro in June, 2003, and for the
explanation below) which has been considered by Jokipii and others.
Cosmic rays have a smooth energy spectrum and an isotropic arrival distribution. Cosmic
rays are scattered as they propagate through the Galaxy by magnetic irregularities on scales
comparable to the gyroradii of the particles, 1014 to 1018 cm.
The power spectrum of the electron density fluctuations in the local interstellar medium
appears to be a power law, with a spectral index of ∼ −11/3, over a range of length scales from
roughly 109 to perhaps 1018 cm. A natural theoretical explanation for magnetic and density
fluctuations on comparable scales is via some kind of magneto-hydro-dynamic phenomenon,
like Alfvén waves.
It is therefore of interest to ask whether IDV results from the same general fluctuations
that are responsible for pulsar scattering, or from “abnormal” density fluctuations that deviate
from the general power-law spectrum. If the latter, one can speculate about the cosmic ray
density within such regions: it could be elevated (due to magnetic trapping of cosmic rays) or
lowered (by magnetic mirror effects). If IDV results from “abnormal” density fluctuations, one
can conclude that the IDV density fluctuations must be rare, as otherwise the arrival directions
of cosmic rays would be more anisotropic.
10
Other connections
Although the cosmic ray flux is dominated by nuclei, there is a primary electron component
(e.g., Torii et al. 2001). While, below the knee, nuclei may travel for a million years or so
within the galaxy before arriving at Earth, electrons lose energy more quickly and so do not
travel as far from their sources. Electrons lose energy as they spiral in magnetic fields, and so
all radio observations of synchrotron radiation are closely related to cosmic rays.
The initial motivation for establishing the Jodrell Bank Observatory was to search for radar
echoes from cosmic ray showers. As Gunn (2003) relates in his recent review, this goal was
never achieved, however, radio emission from cosmic ray showers, a topic undergoing a revival
in interest, was detected in the 1960s.
Finally, Miller Goss pointed out another cosmic ray/radio connection: Eric Greisen, closely
linked with the development of the AIPS data reduction package and the FITS format, is the
son of Kenneth Greisen, the “G” of the GZK cutoff.
11
Conclusions
Although this conference is, as its name indicates, concerned with the variable radio universe,
it has been possible to demonstrate two constant phenomena: the breadth, width, and success
of Dave’s many collaborations, and the fact that all his work over the years has been closely
related to cosmic rays!
Acknowledgements
This research has made extensive use of NASA’s Astrophysics Data System. ISAS is acknowledged for enabling my attendance at this meeting, and John Reynolds and staff are
thanked for hosting it. Joseph Lazio, Roger Clay, and Miller Goss are thanked for their very
helpful contributions, as is Jim Lovell for pointing out the detection by a University of Tasmania cosmic ray detector of an event with a much higher energy than 1020 eV. Finally, Dave
Jauncey is thanked for his enthusiasm and encouragement over the last 17 years.
References
Ahn, E.-J., Medina-Tanco, G., Biermann, P.L. & Stanev, T. 2000, Nucl. Phys. B Proc.
Supp. 87, 417
Biermann, P.L. & Strittmatter, P.A. 1987, ApJ, 322, 643
Clark, B.G., Kellermann, K.I., Bare, C.C., Cohen, M.H., & Jauncey, D.L. 1968, ApJ, 153, 705
Cohen, M.H., Moffet, A.T., Shaffer, D.B., Clark, B.G., Kellermann, K.I., Jauncey, D.L.,
& Gulkis, S. 1969, ApJ, 158, L83
Crawford, D.F., Jauncey, D.L. & Murdoch, H.S. 1970, ApJ, 162, 405
Cronin, J.W. 1999, Rev. Mod. Phys. 71, S165
Drake, F.D., Gundermann, E.J., Jauncey, D.L., Comella, J.M., Zeissig, G.A., Craft Jr., H.D.
1968, Science, 160, 503
Einstein, A. & Straus, E. G. 1945, Rev. Mod. Phys., 17, no. 2–3, pp. 120-124
Elbert, J. & Sommers, P. 1995, ApJ, 441, 151
Erlykin, A.D. & Wolfendale, A.W. 2001, Europhysics News vol. 32, no. 6
Farrar, G.R. & Biermann, P.L. 1998, PRL, 81, 3579
Farrar, G.R. & P.L. Biermann, P.L. 1999, PRL, 83, 2478
Gunn, A.G. 2003, in Radio Astronomy at 70: from Karl Jansky to microjansky,
eds. L. Gurvits, S. Frey, S. Rawlings (EDP Sciences), in press
Gwinn, C.R., Ojeda, M.J., Britton, M.C., Reynolds, J.E., Jauncey, D.L., King, E.A.,
McCulloch, P.M., Lovell, J.E.J., Flanagan, C.S., Smits, D.P., Preston, R.A., & Jones, D.L.
1997, ApJ, 483, L53
Gwinn, C.R., Britton, M.C., Reynolds, J.E., Jauncey, D.L., King, E.A., McCulloch, P.M.,
Lovell, J.E.J., Flanagan, C.S., Preston, R.A. 2000a, ApJ, 531 902
Gwinn, C.R., Reynolds, J.E., Jauncey, D.L., Tzioumis, A.K., Carlson, B., Dougherty, S.,
del Rizzo, D., Hirabayashi, H., Kobayashi, H., Murata, Y., Edwards, P.G., Quick, J.F. H.,
Flanagan, C.S., McCulloch, P.M. 2000b, in Astrophysical Phenomena Revealed by Space
VLBI, eds. H. Hirabayashi, P.G. Edwards, and D.W. Murphy (ISAS) p. 117
Heeschen, D.S. 1982, in IAU Symp. 97 p. 327
Heeschen, D.S. 1984, AJ, 89, 1111
Hillas, A.M. 1984, ARA&A, 22, 425
Hoffman, C. 1999, PRL, 83, 2471
Jauncey, D.L. 1967, Nature, 216, 877
Jauncey, D.L. 1968, ApJ, 152, 647
Jauncey, D.L. 1975, ARA&A, 13, 23
Jauncey, D.L., Tingay, S.J., Preston, R.A., Reynolds, J.E., Lovell, J.E.J., McCulloch, P.M.,
Tzioumis, A.K., Costa, M.E., Murphy, D.W., Meier, D.L., Jones, D.L., Amy, S.W.,
Biggs, J.D., Blair, D.G., Clay, R.W., Edwards, P.G., Ellingsen, S.P., Ferris, R.H.,
Gough, R.G., Harbison, P., Jones, P.A., King, E.A., Kemball, A.J., Migenes, V.,
Nicolson, G.D., Sinclair, M.W., Van Ommen, T., Wark, R.M., & White, G.L. 1995,
Proc. Nat. Acad. Sci. (USA), 92, 11368
Kellermann, K.I., Jauncey, D.L., Cohen, M.H., Shaffer, D.B., Clark, B.G., Broderick, J.,
Rönnäng, B. Rydbeck, O.E.H. Matveyenko, L., Moiseyev, I., Vitkevitch, V.V.,
Cooper, B.F.C., & Batchelor, R. 1971, ApJ, 169, 1
Kellermann, K.I., Clark, B.G., Cohen, M.H., Shaffer, D.B., Broderick, J.J. &
Jauncey, D.L. 1973, ApJ, 179, L141
Lagage, P.O. & Cesarsky, C.J. 1983, A&A, 125, 249
McCusker, C.B.A. 1963, Proc. 8th ICRC (Jaipur), 4, 35
Medina-Tanco, G. 1998, astro-ph/9809219
Morabito, D.D., Preston, R.A. & Jauncey, D.L. 1988, AJ, 95, 1037
Murata, Y. 2000, in Astrophysical Phenomena Revealed by Space VLBI, eds.
H. Hirabayashi, P.G. Edwards, and D.W. Murphy (ISAS) p. 9
Preston, R.A., Morabito, D.D., Williams, J.G., Faulkner, J., Jauncey, D.L. &
Nicolson, G.D. 1985, AJ, 90, 1599
Tingay, S.J., Jauncey, D.L., Reynolds, J.E., Tzioumis, A.K., King, E.A., Preston, R.A.,
Jones, D.L., Murphy, D.W., Meier, D.L., McCulloch, P.M., Ellingsen, S.P., Costa, M.E.,
Edwards, P.G., Lovell, J.E.J., van Ommen, T.D., Nicolson, G.D., Quick, J.F.H.,
Kemball, A.J., Migenes, V., Harbison, P., Jones, P.A., White, G.L., Gough, R.G.,
Ferris, R.H., Sinclair, M.W., & Clay, R.W., 1998, AJ, 115, 960
Torii, S., Tamura, T., Tateyama, N., Yoshida, K., Nishimura, J., Yamagami, T.,
Murakami, H., Kobayashi, T., Komori, Y., Kasahara, K., Yuda, T. 2001, ApJ, 559, 973