A VLA Study of High-redshift GRBs. I. Multiwavelength Observations and Modeling of GRB 140311A

We present the first results from a recently concluded study of GRBs at z greater than or similar to 5 with the Karl G. Jansky Very Large Array (VLA). Spanning 1 to 85.5 GHz and 7 epochs from 1.5 to 82.3 days, our observations of GRB. 140311A are the most detailed joint radio and millimeter observations of a GRB afterglow at z greater than or similar to 5 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-K,E-iso approximate to 8.5 x 10(53) erg expanding into a constant density environment with density, n(0) approximate to 8 cm(-3). The X-ray and radio observations require a jet break at t(jet) approximate to 0.6 jet days, yielding an opening angle of 0(jet) approximate to 4 degrees and a beaming-corrected blast wave kinetic energy of E-K approximate to 2.2 x 10(50) erg. The results from our radio follow-up and multiwavelength 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.