Identifying the Location in the Host Galaxy of the Short GRB 111117A with the Chandra Sub-arcsecond Position

TL;DR

This paper reports on using Chandra's high-precision X-ray observations to locate the host galaxy of short GRB 111117A, revealing its redshift and offset, which aids understanding of short GRB environments.

Contribution

The study demonstrates the effectiveness of Chandra in precisely localizing short GRB afterglows and associating them with host galaxies at high redshift.

Findings

Chandra detected the X-ray afterglow with sub-arcsecond accuracy.

The host galaxy has a redshift of approximately 1.31.

The afterglow is offset by about 8.4 kpc from the host galaxy center.

Abstract

We present our successful Chandra program designed to identify, with sub-arcsecond accuracy, the X-ray afterglow of the short GRB 111117A, which was discovered by Swift and Fermi. Thanks to our rapid target of opportunity request, Chandra clearly detected the X-ray afterglow, though no optical afterglow was found in deep optical observations. The host galaxy was clearly detected in the optical and near-infrared band, with the best photometric redshift of z=1.31_{-0.23}^{+0.46} (90% confidence), making it one of the highest known short GRB redshifts. Furthermore, we see an offset of 1.0 +- 0.2 arcseconds, which corresponds to 8.4 +- 1.7 kpc, between the host and the afterglow position. We discuss the importance of using Chandra for obtaining sub-arcsecond X-ray localizations of short GRB afterglows to study GRB environments.