TITLE:   GCN CIRCULAR
NUMBER:  6921
SUBJECT: GRB 070920A: deep optical observations at the NOT
DATE:    07/10/16 11:32:48 GMT
FROM:    Daniele Malesani at Niels Bohr Inst,Dark Cosmology Center  <malesani@astro.ku.dk>

A.O. Jaunsen (Univ. Oslo), J. Gorosabel (IAA-CSIC), J.P.U. Fynbo, D. 
Malesani, J. Sollerman, Ch. Gall (DARK), T. Morel (Leuven), M.D. 
Stritzinger (DARK), A. Somero, J. Telting, C. Villforth (NOT), report on 
behalf of a larger collaboration:

We observed the field of GRB 070920A (Grupe et al., GCN #6805) in the R 
band with the Nordic Optical Telescope on 2007 September 20.209-20.221 
UT (1.0-1.3 hr after the GRB). Comparison images were taken on 
September 20.216 and again on October 15.135 UT with the same 
telescope, instrumentation and filter. Our images cover 96% of the 
revised BAT error circle(Barbier et al., GCN #6807), missing a small 
region at the northern boundary.

At a mean time of 1.15 hr after the GRB, we do not detect any 
variable object brighter than R=24.3 (calibrated against USNO-B1.0, R1 
magnitudes). There is no evidence for an associated SN on Oct. 15 down 
to the same limit.