We have seen that high velocity neutron stars can produce burst-like behavior. Have high velocity neutron stars ever been seen to produce an event that looks like gamma-ray bursts? The answer is,"yes." The event is the famous 1979 March 5 gamma-ray transient, which I now discuss.
The source of this famous event is SGR 0526-66, which lies in in the Large Magellanic Cloud in the halo of the Milky Way at a distance of 50 kpc. It is associated with the young supernova remnant N49 (Evans et al. 1980, Rothschild, Kulkarni, and Lingenfelter 1994) (see Figure 13). SGR 0526-66 lies far away from the center of the supernova remnant, implying a velocity greater than 1200 km s.
Seventeen bursts have been observed from this source (Mazets et al. 1979, Golenetskii et al. 1984). The distribution of the durations of these bursts overlaps completely with that of gamma-ray bursts (see Figure 14). Let's take a look at the longest of these, the famous 1979 March 5 event itself.
Figure 15 shows the time history of the March 5th event. The burst had an intense spike which lasted s, followed by s of emission which exhibited an 8 s periodicity (Mazets et al 1979). 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. The spectrum of the emission following the intense spike had a characteristic spectral energy keV, typical of soft gamma-ray repeater bursts.
What about the spectrum of the intense spike? Although nine different satellites observed the March 5th event (Evans et al. 1980), the intensity of the spike produced so-called "dead-time" and "pulse pike-up" effects which precluded reliable analyses of the spectrum. Recently, Fenimore et al. (1995) used the power of present-day computers to unravel these effects in the ICE and PVO instruments. They succeeded in accurately determining the spectrum of the spike. The answer? The spectrum of the spike looks just like that of a gamma-ray burst! The spike has a characteristic spectral energy keV, with no soft component (see Figure 16).
Whether the 1979 March 5 event is a gamma-ray burst or a unique event can be argued either way. But in either case, it demonstrates that distant high velocity neutron stars in the Galactic halo can produce events which have the energy, the spectrum, and the duration of gamma-ray bursts. This evidence weighs heavily on the side of the Galactic hypothesis.