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GRB 120521C at z ∼ 6 and the properties of high-redshift γ-ray bursts

Laskar, T, Berger, E, Tanvir, N, Zauderer, BA, Margutti, R, Levan, A, Perley, DA, Fong, WF, Wiersema, K, Menten, K and Hrudkova, M (2014) GRB 120521C at z ∼ 6 and the properties of high-redshift γ-ray bursts. The Astrophysical Journal, 781 (1). ISSN 1538-4357

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We present optical, near-infrared, and radio observations of the afterglow of GRB 120521C. By modeling the multi-wavelength data set, we derive a photometric redshift of z ≈ 6.0, which we confirm with a low signal-to-noise ratio spectrum of the afterglow. We find that a model with a constant-density environment provides a good fit to the afterglow data, with an inferred density of n ≲ 0.05 cm-3. The radio observations reveal the presence of a jet break at t jet ≈ 7 d, corresponding to a jet opening angle of θ jet ≈ 3°. The beaming-corrected γ-ray and kinetic energies are E γ ≈ EK ≈ 3 × 1050 erg. We quantify the uncertainties in our results using a detailed Markov Chain Monte Carlo analysis, which allows us to uncover degeneracies between the physical parameters of the explosion. To compare GRB 120521C to other high-redshift bursts in a uniform manner we re-fit all available afterglow data for the two other bursts at z ≳ 6 with radio detections (GRBs 050904 and 090423). We find a jet break at t jet ≈ 15 d for GRB 090423, in contrast to previous work. Based on these three events, we find that γ-ray bursts (GRBs) at z ≳ 6 appear to explode in constant-density environments, and exhibit a wide range of energies and densities that span the range inferred for lower redshift bursts. On the other hand, we find a hint for narrower jets in the z ≳ 6 bursts, potentially indicating a larger true event rate at these redshifts. Overall, our results indicate that long GRBs share a common progenitor population at least to z ∼ 8. © 2014. The American Astronomical Society. All rights reserved.

Item Type: Article
Uncontrolled Keywords: 0201 Astronomical And Space Sciences, 0305 Organic Chemistry, 0306 Physical Chemistry (Incl. Structural)
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Astrophysics Research Institute
Publisher: American Astronomical Society
Date Deposited: 18 May 2017 10:25
Last Modified: 17 May 2022 09:41
DOI or ID number: 10.1088/0004-637X/781/1/1
URI: https://researchonline.ljmu.ac.uk/id/eprint/6473
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