GCN Circular 5161

Christina C. Thoene, Johan P.U. Fynbo, Jesper Sollerman, Brian L. Jensen,
Jens Hjorth (Dark Cosmology Centre), Pall Jakobsson (Univ. of Hertfortshire),
Sylvio Klose (TLS Tautenburg) report on behalf of a larger collaboration:


We observed the OT position of GRB060505 (GCN 5123
Not found
 
 
), with FORS2/VLT on May
23.28. Comparison with our FORS1/VLT images from May 5.41 shows that the
source has faded from R=21.3 on May 5.41 to R>23 on May 23.28.

At the position of the OT, we detect a bright, star-forming region in the
spiral arm of the possible host galaxy 2dFGRS S173Z112 with redshift
z=0.089 (GCN 5123
Not found
 
 
). Spectroscopy with VLT/FORS2 confirms that this region
is part of the host galaxy. Therefore, it is possible that the source
reported in GCN 5123
Not found
 
 
 for images taken on May 12th, might actually be the
underlying star-forming region.

The observations put a strong limit on the presence of an underlying SN
similar to SN 1998bw at redshift 0.089, which we would expect to have a
magnitude of R=18.4 at the time of our 2nd observation. Therefore, either
there is no associated SN, the SN is about 4 magnitudes fainter than SN
1998bw, it is strongly extinguished, or GRB060505 is not at z=0.089. The
strengths of the Balmer lines and the fact that the host galaxy is seen
close to face on argue against strong dust extinction.

We thank the Paranal staff, in particular Claudio Melo and Rachel Gilmour,
for excellent support.