[vsnet-grb-info 19844] GRB 170921A: NOT optical observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  21909
SUBJECT: GRB 170921A: NOT optical observations
DATE:    17/09/22 07:23:28 GMT
FROM:    Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst  <malesani at dark-cosmology.dk>

D. Malesani (DARK/NBI), K. E. Heintz (Univ. Iceland and DARK/NBI), N. R. 
Tanvir (Univ. Leicester), D. A. Kann (IAA/CSIC), T. Pursimo (NOT), and 
S. Dyrbye (NOT) report on behalf of a larger collaboration:

We observed the field of GRB 170921A (D'Ai et al., GCN 21901) with the 
Nordic Optical Telescope equipped with the AlFOSC imager. Observations 
were carried out with the SDSS r' and z' filters, for a total exposure 
of 900 and 1800 s, respectively.

We did not detect any new object inside or in the proximity of the 
enhanced X-ray error circle (Beardmore et al., GCN 21906). At mean 
epochs 2017 Sep 21.941 and Sep 21.958 UT (8.1 and 8.5 hr after the GRB), 
we report 3-sigma limiting magnitudes r' > 24.3 and z' > 23.3, 
respectively (both AB, calibrated against the Pan-STARRS catalog).

Our non-detections are consistent with the reports by TAROT (Klotz et 
al., GCN 21903), MITSuME (Kuroda et al., GCN 21905), and Nanshan (Feng 
et al., GCN 21907).