Journal Article

Gamma-ray bursts: the isotropic-equivalent-energy function and the cosmic formation rate

Shi-Wei Wu, Dong Xu, Fu-Wen Zhang and Da-Ming Wei

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 423, issue 3, pages 2627-2632
Published in print July 2012 | ISSN: 0035-8711
Published online June 2012 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2012.21068.x
Gamma-ray bursts: the isotropic-equivalent-energy function and the cosmic formation rate

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Gamma-ray bursts (GRBs) are brief but intense emissions of soft gamma-rays, mostly lasting from a few to a few thousand seconds. For these types of high-energy transients, the isotropic-equivalent-energy (Eiso) function may be more scientifically meaningful than the GRB isotropic-equivalent-luminosity (Liso) function, as the traditional luminosity function refers to steady emission much longer than a few thousand seconds. In this work we construct, for the first time, the isotropic-equivalent-energy function for a sample of 95 bursts with measured redshifts (z), and find an excess of high-z GRBs. Assuming that the excess is caused by a GRB luminosity function evolution in a power-law form, we find a cosmic evolution of , which is comparable to that between Liso and z, namely (both 1σ). The evolution-removed isotropic-equivalent-energy function can be reasonably fitted by a broken power law, in which the dim and bright segments are and , respectively (1σ). The cosmic GRB formation rate increases quickly in the region of , remains approximately constant for , and finally decreases with a power index of −3.80 ± 2.16 for z≳4, in good agreement with the cosmic star formation rate observed to date.

Keywords: stars: formation; gamma-ray burst: general

Journal Article.  3330 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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