Journal Article

Simulations on high-<i>z</i> long gamma-ray burst rate

Shu-Fu Qin, En-Wei Liang, Rui-Jing Lu, Jian-Yan Wei and Shuang-Nan Zhang

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 406, issue 1, pages 558-565
Published in print July 2010 | ISSN: 0035-8711
Published online July 2010 | e-ISSN: 1365-2966 | DOI:
Simulations on high-z long gamma-ray burst rate

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Since the launch of Swift satellite, the detections of high-z (z > 4) long gamma-ray bursts (LGRBs) have been rapidly growing, even approaching the very early Universe (the record holder currently is z= 8.3). The observed high-z LGRB rate shows significant excess over that estimated from the star formation history. We investigate what may be responsible for this high productivity of GRBs at high-z through Monte Carlo simulations, with effective Swift/Burst Alert Telescope (BAT) trigger and redshift detection probabilities based on current Swift/BAT sample and Compton Gamma-ray Observatory/Burst and Transient Source Experiment LGRB sample. We compare our simulations to the Swift observations via log N– log P, peak luminosity (L) and redshift distributions. In the case that LGRB rate is purely proportional to the star formation rate, our simulations poorly reproduce the LGRB rate at z > 4, although the simulated log N– log P distribution is in good agreement with the observed one. Assuming that the excess of high-z GRB rate is due to the cosmic metallicity evolution or unknown LGRB rate increase parametrized as (1 +z)δ, we find that although the two scenarios alone can improve the consistency between our simulations and observations, incorporation of them gives much better consistency. We get 0.2 < ε < 0.6 and δ < 0.6, where ε is the metallicity threshold for the production of LGRBs. The best consistency is obtained with a parameter set (ε, δ) = (∼ 0.4, ∼ 0.4), and BAT might trigger a few LGRBs at z≃ 14. With increasing detections of GRBs at z > 4 (∼15 per cent of GRBs in current Swift LGRB sample based on our simulations), a window for very early Universe is opening by Swift and up-coming space-based multiband astronomical variable object monitor missions.

Keywords: instrumentation: detectors; stars: evolution; stars: formation; gamma-ray burst: general; stars: luminosity function, mass function; galaxies: high-redshift

Journal Article.  4882 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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