GRB 120521C at z ∼ 6 and the properties of high-redshift γ-ray bursts
- Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
- Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH (United Kingdom)
- Department of Physics, University of Warwick, Coventry CV4 7AL (United Kingdom)
- Department of Astronomy, California Institute of Technology, MC 249-17, 1200 East California Boulevard, Pasadena, CA 91125 (United States)
- Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn (Germany)
- Isaac Newton Group of Telescopes, Apartado de Correos 321, E-387 00 Santa Cruz de la Palma, Canary Islands (Spain)
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{sup –3}. The radio observations reveal the presence of a jet break at t {sub jet} ≈ 7 d, corresponding to a jet opening angle of θ{sub jet} ≈ 3°. The beaming-corrected γ-ray and kinetic energies are E {sub γ} ≈ E{sub K} ≈ 3 × 10{sup 50} 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 {sub 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.
- OSTI ID:
- 22348193
- Journal Information:
- Astrophysical Journal, Vol. 781, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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