Empirical constraints on cosmological gamma-ray bursts.

摘要

Gamma-Ray Bursts (GRBs) have baffled astronomers for nearly three decades. Great strides have been made in recent years in determining the distances and detecting longer-wavelength counterparts to these events, as well as in modeling their behavior after the initial energy release. However, the ultimate progenitors of the most violent explosions in the universe have yet to be identified. Hence it is important to make the most of the available data to derive empirical, largely model-independent constraints on the burst sources. In this thesis, I consider several such constraints. First, I place limits on the expansion Lorentz factor γ and related source properties, and apply these constraints statistically to the burst population as a whole. In general, I find that γ > 100 for the average burst, but some bursts have stronger and some have weaker limits. Second, I consider a way of constraining the degree of beaming in GRB explosions by looking for an excess of prompt x-ray events which are viewed off-axis. I find that with instruments an order of magnitude more sensitive than those flown on board the old Ariel V satellite in the 1970's, it should be possible to place significant limits on the beaming. Third, I predict the detection rate and source counts of optical and infrared GRB afterglows in supernova searches, and compare the results with those obtained for supernovae themselves. We find that the two classes of events should be detectable in comparable numbers at magnitudes around K = 18. Finally, I consider the detectability of older ($\gtrsim$ 104 yr) GRB remnants at radio frequencies. While the telltale signature of old remnants may occur at higher frequencies, they should be easiest to detect in the radio because of the low degree of contamination from the sky and the host galaxies.