Tests and Consequences of Disk plus Halo Models of Gamma-Ray Burst Sources
Smith, I. A.
The gamma-ray burst observations made by the Burst and Transient Source
Experiment (BATSE) and by previous experiments are still consistent with
a combined Galactic disk (or Galactic spiral arm) plus extended Galactic halo
model.
Testable predictions and consequences of the disk plus halo model are
discussed here; tests performed on the expanded BATSE database in the
future will constrain the allowed model parameters and may eventually rule
out the disk plus halo model.
Using examples, it is shown that if the halo has an appropriate edge, BATSE
will never detect an anisotropic signal from the halo of the Andromeda galaxy.
A prediction of the disk plus halo model is that the fraction of the bursts
observed to be in the `disk' population rises as the detector sensitivity
improves.
A careful reexamination of the numbers of bursts in the two populations for
the pre-BATSE databases could rule out this class of models.
Similarly, it is predicted that different satellites will observe different
relative numbers of bursts in the two classes for any model in which there
are two different spatial distributions of the sources, or for models in
which there is one spatial distribution of the sources that is sampled to
different depths for the two classes.
An important consequence of the disk plus halo model is that for the
birthrate of the halo sources to be small compared to the birthrate of the
disk sources, it is necessary for the halo sources to release many orders
of magnitude more energy over their bursting lifetime than the disk sources.
The halo bursts must also be much more luminous than the disk bursts; if this
disk-halo model is correct, it is necessary to explain why the disk sources
do not produce halo-type bursts.
Status:
1995, ApJ, 444, 686.
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