[vsnet-grb-info 6617] GRB 080913: VLT/FORS2 observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  8221
SUBJECT: GRB 080913: VLT/FORS2 observations
DATE:    08/09/13 10:58:48 GMT
FROM:    Paul Vreeswijk at Dark Cosmology Centre,U.of Copenhagen  <pmv at dark-cosmology.dk>

P.M. Vreeswijk, J.P.U. Fynbo, D. Malesani (DARK/NBI) report on behalf 
of a larger collaboration:

The field of GRB 080913 (Swift trigger 324561; Schady et al., GCN 
#8217) was observed in target-of-opportunity mode with VLT+FORS2 using 
the imaging sequence RzIVBR, starting at 7:31 UT on September 13, 2008, 
i.e. 45 minutes after the GRB.

In the z-band image a faint source is detected within the Swift/XRT 
error circle, with magnitude z(AB) = 23.1 (based on a very preliminary 
calibration), while this object is not detected in any of the other 
optical filters. Comparison with the z-band magnitude reported by Rossi 
et al. (GCN #8218) suggests that the object has faded between 3 and 45 
minutes after the burst, and therefore is likely the afterglow of GRB 
080913.

We are very grateful for the excellent support by the Paranal 
observatory staff, in particular Rachel Gilmour and Heidi Schmidt.