[vsnet-grb-info 2765] GRB 060116 HST observations

[GCN Circulars]

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  <nrt at ast.cam.ac.uk>

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.