TITLE:   GCN CIRCULAR
NUMBER:  31300
SUBJECT: GRB 211106A: Third HST Observation
DATE:    21/12/24 20:01:28 GMT
FROM:    Charles Kilpatrick at Northwestern U  <ckilpatrick@northwestern.edu>

C. D. Kilpatrick (Northwestern), E. Berger (Harvard), and W. Fong (Northwestern) report on behalf of a larger collaboration:

"We obtained a third observation at the site of the short GRB 211106A (GCNC #31049) with the Hubble Space Telescope starting on 2021 December 24.35 (48.15 days post-trigger, 29.0 days after Visit 1 - GCNC #31146, and 22.9 days after Visit 2 - GCNC #31157) using ACS/F814W for 2 orbits and WFC3/F110W for 2 orbits, as part of program 16303 (PI: Berger).  

The source identified in both our previous HST observations and near the reported CXO position of GRB 211106A (GCNC #31145) is still detected, with unchanged magnitudes of m(F110W) ~ 25.6 mag and m(F814W) ~ 25.7 mag.  We also detect an extension to the north of the source in stacked F814W imaging (Visit 1 + Visit 3) as previously noted in the F110W imaging (GCNC #31049). The lack of any change over this 29-day baseline, the relatively flat m(F814W)-m(F110W) color, the extension in both bands, and the small offset from the CXO position (GCNC #31145) support the hypothesis that this source is the more likely host galaxy of GRB 211106A."