TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4602 SUBJECT: GRB 060116 HST observations DATE: 06/01/26 13:02:46 GMT FROM: Nial Tanvir at IofA U.Cambridge N. R. Tanvir, A. J. Levan, R. S. Priddey (U. Hertfordshire) A. S. Fruchter (STScI), J. Hjorth (DARK Cosmology Centre) report on behalf of a larger collaboration: We observed the field of GRB060116 (Campana et al . GCN 4539, Kocevski et al. GCN 4528) with HST on Jan 23 and Jan 24. We clearly detect the afterglow in NICMOS/F160W, but only obtain an upper limit in ACS/F775W. A preliminary limit on the I-H vegamag colour is > 5.5. If the suggested redshift of z=6.6 (Grazian et al. GCN 4545) is correct then very little flux would be expected in the F775W observation, consistent with our results. However, we note that the location of this GRB is only about a degree east of the Orion Nebula, and although the extinction in this area is not very high, it is patchy and we caution that the Schlegel et al. (1998 ApJ 500 525) extinction estimate for the burst position of Av=1.20 (implying E(I-H)~0.5), may not be reliable. A map of extinction in Orion based on optical star counts by Cambresy (1999 A&A 345 965) suggests a higher extinction Av between 2 and 2.5, but again this is at best an average for the area. A similar star-count analysis available at URL http://darkclouds.term.jp, also indicates Av between 2.2 and 2.4 at the position of the burst. The inferred X-ray column (Campana et al. GCN 4529) if interpretted as purely local extinction gives Av around 4.3+/-1.3, apparently higher than any of the above.