[vsnet-grb-info 20843] GRB 180705A: OSN observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  22941
SUBJECT: GRB 180705A: OSN observations
DATE:    18/07/11 19:25:41 GMT
FROM:    Alexander Kann at IAA-CSIC  <kann at iaa.es>

D. A. Kann, L. Izzo (both HETH/IAA-CSIC), and A. Sota (IAA/CSIC) report 
on behalf of HETH:

We observed the field of GRB 180705A (Stamatikos et al., GCN #22902) 
with the 1.5-m OSN telescope in Granada, Spain.

We obtained 20 x 300 s images in the Ic band centered at 0.262416 days 
(6.3 hrs) after the GRB.

At the XRT position of the GRB (Goad et al., GCN #22906), there is a 
possible faint source, formally detected at Ic (Vega) = 23.6 +/- 0.2 
mag. We note, however, that the background of the image is structured 
because of the proximity of the bright star HD 123921 (V ~ 9 mag), 
therefore the detection may be spurious. The formal 3 sigma upper limit 
is Ic > 24 mag, also possibly overestimated.

Even if the source we detect is not real, any afterglow of this GRB is 
clearly very faint, in agreement with other non-detection reports 
(Lipunov et al., GCN #22904, Watson et al., GCN #22911, Breeveld et al., 
GCN #22912, Mazaeva et al., GCN #22913, Bikmaev et al., GCN #22929).

The field was calibrated against SDSS secondary standard stars using the 
transformation of Lupton (2005).