TITLE:   GCN CIRCULAR
NUMBER:  23461
SUBJECT: GRB 181123B: Keck further near-infrared imaging
DATE:    18/11/27 01:09:10 GMT
FROM:    Kerry Paterson at North Western U.  <kerry.paterson@northwestern.edu>

K. Paterson, W. Fong (Northwestern), K. De (Caltech), K. Alexander, D. Coppejans, A. Hajela, R. Margutti, and G. Terreran (Northwestern) report:

"We observed the field of the short-duration GRB 181123B (Lien et al., GCN 23432) with the Multi-Object Spectrometer For Infra-Red Exploration (MOSFIRE) mounted on the 10-m Keck I telescope, starting on 2018 November 26 at 14:57:43 UT, 1.94 days after our previous MOSFIRE observations (Paterson et al. GCN 23440) and 3.38 days after the burst. We obtained 2142-sec of observations in the J-band in 0.7" seeing and clear conditions.

We detect a NIR source that is clearly extended, with a brightness and position consistent with our previous observations (Paterson et al. GCN 23440) and with the Gemini optical source position (Fong et al. GCN 23439). Image subtraction between our MOSFIRE observations also yields no residuals in or around the XRT position (Evans et al. GCN 23433; Osborne et al. GCN 23434) or the position of the optical source. Given the lack of residuals and the extended nature of the NIR source, we propose this as the host galaxy of GRB 181123B. We also place a 3-sigma upper limit of J>23.3 mag (AB, for epoch 1 at 9.2 hr post-burst) on afterglow emission from GRB 181123B.

We thank the Keck staff for their assistance with these ToO observations."