A VLA Study of High-redshift GRBs I - Multi-wavelength Observations and Modeling of GRB 140311A

TL;DR

This study presents detailed multi-wavelength radio and millimeter observations of a high-redshift gamma-ray burst, modeling its afterglow to understand its environment, energetics, and jet properties, and suggesting high-redshift GRBs may be more tightly beamed.

Contribution

First detailed joint radio and millimeter observations of a high-redshift GRB, combined with multi-wavelength modeling to analyze its environment and jet characteristics.

Findings

Jet break at 0.6 days indicating a narrow jet opening angle

Beaming-corrected kinetic energy of approximately 2.2×10^{50} erg

No compelling evidence for reverse shock emission

Abstract

We present the first results from a recently concluded study of GRBs at $z\gtrsim5$ with the Karl G. Jansky Very Large Array (VLA). Spanning $1$ to $85.5$ GHz and 7 epochs from 1.5 to 82.3 d, our observations of GRB 140311A are the most detailed joint radio and millimeter observations of a GRB afterglow at $z\gtrsim5$ to date. In conjunction with optical/near-IR and X-ray data, the observations can be understood in the framework of radiation from a single blast wave shock with energy $E_{\rm K,iso}\approx8.5\times10^{53}$ erg expanding into a constant density environment with density, $n_0\approx8\,{\rm cm}^{-3}$. The X-ray and radio observations require a jet break at $t_{\rm jet}\approx0.6$ d, yielding an opening angle of $\theta_{\rm jet}\approx4^{\circ}$ and a beaming-corrected blast wave kinetic energy of $E_{\rm K}\approx2.2\times10^{50}$ erg. The results from our radio follow-up and multi-wavelength modeling lend credence to the hypothesis that detected high-redshift GRBs may be more tightly beamed than events at lower redshift. We do not find compelling evidence for reverse shock emission, which may be related to fast cooling driven by the moderately high circumburst density.