Discovery of Radio Afterglow from the Most Distant Cosmic Explosion

TL;DR

This paper reports the discovery of radio afterglow from the most distant known gamma-ray burst at redshift 8.3, analyzing its properties and implications for early universe progenitors and future radio observations.

Contribution

First detection of radio afterglow from a gamma-ray burst at redshift 8.3, providing insights into high-redshift GRB properties and progenitor models.

Findings

Radio afterglow detected at z=8.3, the highest known redshift.

The burst's energy and afterglow are similar to other high-redshift GRBs.

Early radio emission likely includes reverse shock component.

Abstract

We report the discovery of radio afterglow emission from the gamma-ray burst GRB 090423, which exploded at a redshift of 8.3, making it the object with the highest known redshift in the Universe. By combining our radio measurements with existing X-ray and infrared observations, we estimate the kinetic energy of the afterglow, the geometry of the outflow and the density of the circumburst medium. Our best fit model is a quasi-spherical, high-energy explosion in a low, constant-density medium. \event had a similar energy release to the other well-studied high redshift GRB 050904 ($z=6.26$), but their circumburst densities differ by two orders of magnitude. We compare the properties of \event with a sample of GRBs at moderate redshifts. We find that the high energy and afterglow properties of \event are not sufficiently different from other GRBs to suggest a different kind of progenitor, such as a Population III star. However, we argue that it is not clear that the afterglow properties alone can provide convincing identification of Population III progenitors. We suggest that the millimeter and centimeter radio detections of \event at early times contained emission from a reverse shock component. This has important implications for the detection of high redshift GRBs by the next generation of radio facilities.