Dai 2008 Swift暴的光度函数

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Title:		Intensity Distribution and Luminosity Function of the Swift Gamma-Ray Bursts
Authors:		Dai, Xinyu
Publication:		eprint arXiv:0812.4466
Publication Date:		12/2008
Origin:		ARXIV
Keywords:		Astrophysics
Comment:		11 pages, 3 figures, submitted to ApJ Letters
Bibliographic Code:		2008arXiv0812.4466D

Abstract

Using the sample of long Gamma-ray bursts detected by Swift-BAT before June 2007, we measure the Log N - Log P distribution of the Swift bursts. Compared with the BATSE sample, we find that the two distributions are consistent after correcting the bandpass difference suggesting that the two instruments are sampling the same population of bursts. We also compare the Log N - Log P distributions for sub-samples of the Swift bursts, and find evidence for a deficit (99.75% confident) of dark bursts at high peak flux levels suggesting different redshift or Gamma-ray luminosity distributions. The consistency between the Log N - Log P distributions for the optically detected bursts with and without redshift measurements indicates that the current sample of the Swift bursts with redshift measurements, although selected heterogeneously, represents a fare sample of the none-dark bursts. We calculate the luminosity functions of this sample in two redshift bins (z<1>1), and find a broken power-law is needed to fit the low redshift bin, where dN/dL \propto L^{-1.30\pm0.06} at the high luminosity range (L_{peak} > 5E48 erg/s) and dN/dL \propto L^{-2.5\pm0.3} at the low luminosity end confirming the existence of a population of low luminosity GRBs. For the high redshift bin, the normalization of the luminosity function is not higher than the low redshift counterpart challenging the hypothesis that GRB rate follows the star formation rate.

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