I have summarized observational results and theoretical calculations which provide evidence about the distance scale. First, I described the recent discovery that many neutron stars have high enough velocities to escape from the Milky Way. These high velocity neutron stars form a distant, previously unknown Galactic "corona." This distant corona is isotropic when viewed from Earth, and consequently, the population of neutron stars in it can easily explain the angular and brightness distributions of the BATSE bursts. If this were all of the evidence that we considered we could not distinguish between the cosmological and Galactic hypotheses. I contended that we can go further, by considering other important pieces of evidence.
I drew attention to the many similarities between soft gamma-ray repeaters, which are known to be high velocity neutron stars, and gamma-ray bursts. I pointed out that the source of the famous 1979 March 5 event, which is a high velocity neutron star 50 kpc away from us, demonstrates that high velocity neutron stars are capable of producing bursts which have the energy, the duration, and the spectrum of gamma-ray bursts. Finally, I commented that high velocity neutron stars in a distant Galactic corona can account for cyclotron lines and repeating, and naturally explain the absence of bright optical counterparts in gamma-ray burst error boxes, whereas all of these present major difficulties for cosmological models.
I conclude that when we consider all of the evidence, it adds up to a strong case for the Galactic hypothesis (see Table 1).
ACKNOWLEDGEMENTS
I would like to acknowledge the help of my secretary, Johanna Darden, and members and former members of my research group at Chicago, including Jeff Benensohn, Peter Freeman, Mike Isenberg, Lucia Munoz-Franco, Francois Palaez, Paul Ricker, and especially, Tomek Bulik, Paolo Coppi, Cole Miller, and Jean Quashnock, in preparing for this debate. I would also like to thank my colleagues at Chicago for their advice and counsel, including David Schramm, Michael Turner, and especially Bob Rosner. Finally, and particularly, I would like to thank Ed Fenimore, who served as an invaluable "sparring partner" in preparing for this debate, and who emphasized the importance of weighing all of the evidence as part of the scientific process.
FIGURE CAPTIONS
Figure 1. Sky map of the first 1005 gamma-ray bursts observed by
BATSE. Of these, 485 are from the second BATSE catalog and have
positional uncertainties of about 
. The remainder have
preliminary positions or are affected by gaps in the telemetry stream,
and have more uncertain positions. (From Briggs et al. 1995.)
Figure 2. Sky map of 1005 bursts from a Galactic corona of high velocity neutron stars. This map demonstrates that a non-cosmological population of objects can also account for the BATSE sky distribution of gamma-ray bursts. (After Bulik and Lamb 1995.)
Figure 3. Side view of the Milky Way. The Galactic bulge and disk are clearly visible; the dark lane along the plane of the Galaxy is the result of dust. Also shown are the Sun, the globular clusters which surround the Galactic disk, and the trajectories of high velocity neutron stars which are escaping from the Milky Way. These high velocity neutron stars form a previously unknown Galactic "corona." The corona contains an ample population of neutron stars which appears isotropic when viewed from Earth. Many scientists believe that this population of distant neutron stars is the source of gamma-ray bursts.
Figure 4. False-color radio image of the supernova remnant G5.4 - 1.2
and the young radio pulsar PSR 1757-24. The pulsar has a velocity of
at least 1300 - 1700 km s
away from the plane of the Galaxy.
Pulsars like this reach a distance of 100 kpc in about 70 Myr, and form
a distant, previously unknown halo of neutron stars around the Milky
Way. (After Frail, Kassim, and Weiler 1994.)
Figure 5. Histogram of pulsar transverse velocities derived from associations between young radio pulsars and young supernova remnants. Half have transverse velocities and are escaping from the Galaxy; these produce an ample population of sources which appear isotropic when viewed from the Earth. (From Frail, Goss, and Whiteoak 1994.)
Figure 6. Color picture of high velocity neutron stars streaming away from the Milky Way, as viewed by an observer outside the galaxy. (After Bulik and Lamb 1995.)
Figure 7. Sky map of 1005 bursts from a Galactic corona of high velocity neutron stars and sky map of the first 1005 BATSE bursts. It is impossible to tell the two maps apart, demonstrating that cosmological sources are not the only distant objects that can account for the BATSE sky distribution of gamma-ray bursts. (After Bulik and Lamb 1995.)
Figure 8. Brightness distribution of bursts from a Galactic corona of high velocity neutron stars and brightness distribution of the bursts in the second BATSE catalog. It is impossible to tell the two distributions apart, demonstrating that cosmological sources are not the only objects that can account for the BATSE brightness distribution of gamma-ray bursts. (After Bulik and Lamb 1995.)
Figure 9. Comparison of the brightness distribution of bursts from a Galactic corona of high velocity neutron stars (thin line) and the brightness distribution of both BATSE and PVO gamma-ray bursts (thick lines) (from Fenimore et al. 1993). (After Bulik and Lamb 1995.)
Figure 10. Sky distribution and brightness distribution of bursts from a Galactic corona of high velocity neutron stars for BATSE sampling distances ranging from 100 - 600 kpc. (After Bulik, Coppi, and Lamb 1995.)
Figure 11. Comparison of the durations of soft gamma-ray repeater bursts and gamma-ray bursts. Soft gamma-ray repeaters are known to be high velocity neutron stars that lie at distances of 10's of kpc.
Figure 12. Comparison of the hardness ratios (i.e., characteristic spectral energies) of soft gamma-ray repeater bursts and short ( s) gamma-ray bursts. Soft gamma-ray repeaters are known to be high velocity neutron stars that lie at distances of 10's of kpc. (After Kouveliotou 1993.)
Figure 13. False-color X-ray image of the supernova remnant N49 in the
Large Magellanic Cloud, which lies at a distance of 50 kpc from us.
Superimposed on the image is the error box for SGR 0526-66, the source
of the 1979 March 5 gamma-ray transient and sixteen recurrences of it.
The error box lies far away from the center of the supernova remnant,
implying that the neutron star has a velocity greater than
km s
.
There is little doubt that the 1979 March 5 event came from
a high velocity neutron star 50 kpc away from us. (After Rothschild,
Kulkarni, and Lingenfelter 1994).
Figure 14. Comparison of the durations of the 17 bursts from SGR 0526-66 and gamma-ray bursts. SGR0526-66 is a high velocity neutron star 50 kpc away from us.
Figure 15. Time history of the famous 1979 March 5 gamma-ray transient. The association with the supernova remnant N49 and the 8 s periodicity leave little doubt that this object is a neutron star. The existence of pulsations implies a strong magnetic field. (After Mazets et al. 1979.)
Figure 16. Comparison of the spectrum of the initial spike of the famous 1979 March 5 gamma-ray transient and the spectra of gamma-ray bursts. The March 5th event demonstrates that neutron stars kpc away are capable of producing gamma-ray bursts. (After Fenimore, Klebesadel, and Laros 1995.)
Figure 17. Photon number spectra of GB870303 and GB880205. The equally-spaced lines are seen in other neutron star sources and are easily explained as cyclotron scattering in a strong magnetic field. (After Fenimore et al. 1988 and Graziani et al. 1992.)
Figure 18. Photon number spectra of four accretion-powered pulsars. Notice the equally-spaced lines, which are similar to those in gamma-ray bursts. (After Makishima and Mihara 1992.)
Figure 19. Sky distribution of those bursts in the first BATSE catalog which have another burst within , highlighting the evidence for gamma-ray burst repeating. Repeating sources appear as clusters of bursts on the sky because the positions of the bursts are known only to about (From Quashnock and Lamb 1994.)
Figure 20. Time dilation versus redshift 
predicted for gamma-ray
bursts, assuming that the bursts are cosmological. If the reported time
stretching of a factor of two were attributed to cosmological time
dilation, the sources would have to lie at a redshift 
and
they would be orphans. If they were to lie closer, most of the
reported time stretching would have to be intrinsic to the source.
(From Fenimore and Bloom 1995.)
Figure 21. Interplanetary Network location for GB790406 showing the absence of any bright galaxy in the error box. (After Motch et al. 1985.)
Figure 22. Interplanetary Network location for GB791116 showing the absence of any bright galaxy in the error box. The bright object near the lower left hand boundary of the error ellipse and the faint object inside and toward the upper right hand boundary of the error ellipse are nearby stars. (After Schaefer 1992.)
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