Ep-Eiso correlation in a multiple subjet model of gamma-ray bursts

Toma Kenji

Yamazaki Ryo

Nakamura Takashi

Astrophysical Journal

We perform Monte Carlo simulations to study the Ep-E iso correlation in the context of a multiple-subjet model (or inhomogeneous jet model) for γ-ray bursts (GRBs), X-ray-rich GRBs (XRRs), and X-ray flashes (XRFs). For a single subjet, we find that Ep ∝ Eiso0.4 for large viewing angles. For the multiple-subjet model in which all the subjets have the same intrinsic properties, off-axis events show Ep ∝ Eisoa with 0.4 < a < 0.5. If the intrinsic properties of the subjets are distributed so that on-axis emission of each subjet follows a correlation Ep ∝ Liso1/2, we obtain the Amati correlation (Ep ∝ Eiso1/2) over 3 orders of magnitude in E p. Although the scatter around the Amati correlation is large in the simulation, the results are consistent with the observed properties of GRBs with known redshifts and the BASTE GRBs with pseudoredshifts derived from the lag-luminosity correlation. We also calculate the event rates, the redshift distributions, and the T90 duration distributions of GRBs, XRRs, and XRFs, which can be detected by HETE-2, assuming that the source redshift distribution is in proportion to the cosmic star formation rate. It is found that the event rates of the three classes are comparable, that the average redshift of the XRRs is a little larger than those of the GRBs and the XRFs, and that short XRRs arise when a single subjet is viewed off-axis or viewed on-axis with slightly high redshift. © 2005. The American Astronomical Society. All rights reserved.

gamma rays

theory

bursts

Astronomy. Space sciences [ 440 ]

eng

University of Chicago Press

Copyright (c) 2005 The American Astronomical Society

[ISSN] 0004-637X

[DOI] 10.1086/497388

[DOI] http://dx.doi.org/10.1086/497388