Francisco 2008 Low-Luminosity Gamma-Ray Bursts as a Distinct GRB Population:A Monte Carlo Analysis is much popular than high-lominosity ones

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LL-GRBs is $\sim$ 100 Gpc$^{-3}$ yr$^{-1}$ at the break luminosity, much larger than that of HL-GRBs.

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· arXiv e-print (arXiv:0801.4751)

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Title:		Low-Luminosity Gamma-Ray Bursts as a Distinct GRB Population:A Monte Carlo Analysis
Authors:		Virgili, Francisco; Liang, Enwei; Zhang, Bing
Publication:		eprint arXiv:0801.4751
Publication Date:		01/2008
Origin:		ARXIV
Keywords:		Astrophysics
Comment:		20 pages, 9 figures, 3 tables
Bibliographic Code:		2008arXiv0801.4751V

Abstract

The intriguing observations of {Swift}/BAT GRB 060218 and CGRO/BATSE burst 980425, both with much lower luminosity and redshift compared to other observed bursts, lead naturally to the question whether these low-luminosity (LL) bursts constitute a separate population from high-luminosity (HL) bursts. Utilizing Monte Carlo simulations we compare various single-component luminosity function (LF)models (single power law or broken power law) with the two-component luminosity function model proposed by Liang et al. Using various criteria, we demonstrate that the single-component LF models have great difficulty in simultaneously reproducing both the high local LL-GRB rate and the oberved distributions of redshift, luminosity, and $\log N-\log P$ for HL-GRBs. We argue that the two-component LF model is necessary, and we use the observed BATSE and Swift $\log N-\log P$ distributions to add constrains to the LL and HL-LF parameters. The LL-LF can be modeled by a smoothed, broken power law with a break at around $10^{47}$ erg s$^{-1}$, dropping steeply above this luminosity. The local rate of LL-GRBs is $\sim$ 100 Gpc$^{-3}$ yr$^{-1}$ at the break luminosity, much larger than that of HL-GRBs. The recently discovered peculiar X-ray transient XRF 080109/SN 2008D strengthens this conclusion, and requires that the LL-population LF extends further down in luminosity with a probably even higher local rate at lower luminosities.

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