TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4841 SUBJECT: GRB 060121: HST observations DATE: 06/02/28 01:02:32 GMT FROM: Andrew Levan at U.of Leicester A.J. Levan, N.R. Tanvir (University of Hertfordshire), A. Fruchter (STScI), J. Fynbo, J. Hjorth (Dark Cosmology Centre), E. Rol (University of Leicester), D. Bersier (Liverpool JMU), J. Gorosabel, A.J. Castro-Tirado (IAA-CSIC Granada) report for a larger collaboration: We observed the location of the HETE-2 short hard burst GRB 060121 (Prigozhin et al. GCN 4551; Malesani et al. GCN 4561) with HST on 27 February 2006 using both ACS and NICMOS. Approximately 4500 s of observations in each of F606W and F160W were obtained. Performing astrometry between these images and those obtained at the WIYN (Levan et al. GCN 4562) reveals no evidence for an afterglow to R>28, although the position of the burst lies close to a faint red galaxy with F160W =24.0, F606W =26.8. The morphology of the galaxy is long and thin, possibly an edge on disk. If this object is the host galaxy of GRB 060121 then it is relatively red compared to the hosts of long bursts, and there are also several other galaxies with very red colours within 30" of the burst position. Short bursts have been observed in a greater variety of host galaxies, but in this case, the faintness of the galaxy in both the optical and IR favour a higher redshift than has been measured for most short bursts to date (which is also consistent with the red colour of the afterglow). We thank Matt Mountain for using Director's Discretionary Time to observe GRB 060121. Further analysis is ongoing.