[vsnet-grb-info 12427] GRB 120923A: Gemini afterglow detection, high-z candidate

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  13802
SUBJECT: GRB 120923A: Gemini afterglow detection, high-z candidate
DATE:    12/09/23 10:33:17 GMT
FROM:    Andrew Levan at U.of Leicester  <A.J.Levan at warwick.ac.uk>

A.J. Levan (U. Warwick), D.A. Perley (Caltech), N.R. Tanvir (U. Leicester) and A. Cucchiara (UCSC) report for a larger collaboration:

"We observed the location of GRB 120923A (Yershov et al. GCN 13796) with Gemini-North, beginning approximately 1.4 hours after the burst. Observations were obtained in riz (with GMOS) and YJHK (with NIRI). In our optical and Y-band observations we detect no source in the refined XRT error circle (Goad et al. GCN 13801), with a preliminary z-band limit of z~24. However, in our JHK observations we clearly detect a source at a location of

RA(J2000): 20:15:10.78
DEC(J2000): 06:13:16.3
(uncertainty ~0.5")

Which is seen to fade in two epochs of J-band observations separated by ~3 hours, confirming it as the counterpart of GRB 120923A. The colours of this source in the IR are blue, with H-K~0.1 mag. This is strongly suggestive of a break between the Y and J-band, similar to GRB 090423, and may indicate that GRB 120923A lies at z~8.

We thank Michael Hoenig for excellent support for these observations.

Further observations are ongoing."