Journal Article

The luminosity function of <i>Swift</i> long gamma-ray bursts

Xiao-Feng Cao, Yun-Wei Yu, K. S. Cheng and Xiao-Ping Zheng

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 416, issue 3, pages 2174-2181
Published in print September 2011 | ISSN: 0035-8711
Published online September 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2011.19194.x
The luminosity function of Swift long gamma-ray bursts

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The accumulation of Swift observed gamma-ray bursts (GRBs) has gradually made it possible to directly derive a GRB luminosity function (LF) from the observational luminosity distribution. However, two complexities are involved: (i) the evolving connection between GRB rate and cosmic star formation rate; and (ii) observational selection effects due to telescope thresholds and redshift measurements. With a phenomenological investigation of these two complexities, we constrain and discriminate two popular competing LF models (i.e. the broken-power-law LF and the single-power-law LF with an exponential cut-off at low luminosities). As a result, we find that the broken-power-law LF may be more favoured by observations, with a break luminosity Lb= 2.5 × 1052 erg s−1 and prior- and post-break indices ν1= 1.72 and ν2= 1.98. Regarding an extra evolution effect expressed by a factor (1 +z)δ, if the metallicity of GRB progenitors is lower than ∼0.1 Z as expected by some collapsar models, then there may be no extra evolution effect other than the metallicity evolution (i.e. δ approaches zero). Alternatively, if we remove the theoretical metallicity requirement, then a relationship between the degenerate parameters δ and Zmax can be found, very roughly, δ∼ 2.4(Zmax /Z− 0.06). This indicates that extra evolution could become necessary for relatively high metallicities.

Keywords: gamma-ray burst: general

Journal Article.  5134 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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