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C. Graziani, D. Q. Lamb, T. Q. Donaghy (Department of Astronomy & Astrophysics, University of Chicago)
HETE-II and BSAX have produced a sample of GRBs and XRFs with known redshifts and Epk. This sample provides three important empirical constraints on the nature of the source jets: Log Eiso is approximately uniformly distributed over several orders of magnitude; the inferred prompt energy Log E\gamma is narrowly distributed; and the Amati relation holds between Eiso and Epk.
We explore here the specific implications of these constraints for the angular emission profiles of GRB jets during the internal shock phase. We infer the underlying angular profiles from the first two of the above constraints assuming all jets have the same profile and total energy, and show that such ``universal jet'' models cannot satisfy both constraints.
We introduce a general and efficient method for calculating relativistically-beamed emission distributions and Epk distributions for arbitrary smooth angular jet profiles. This method is useful for calculating GRB/XRF emission in population-synthesis Monte Carlo simulations. Here we use the method to exhibit the behavior of Epk, Eiso, and E\gamma for several interesting GRB/XRF jet profiles.
We then proceed to explore the range of profile shapes and parameters for which the relationship between Epk and Eiso can approximate the Amati relation for the full energy range from GRBs to XRFs, under the ``universal jet'' assumption.
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Bulletin of the American Astronomical Society, 37 #2
© 2005. The American Astronomical Soceity.