[vsnet-grb-info 25209] GRB 200303A: NOT optical observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  27309
SUBJECT: GRB 200303A: NOT optical observations
DATE:    20/03/03 15:25:21 GMT
FROM:    Luca Izzo at IAA-CSIC  <luca.izzo at gmail.com>

D. Xu (NAOC), L. Izzo (DARK/NBI),  D. B. Malesani (DTU Space), A.A. Djupvik (NOT), T. Pursimo (NOT) report on behalf of a larger collaboration:
We observed GRB 200303A (Fermi GBM team, GCN 27294, Cenko et al., GCN 27297, Asaoka et al., GCN 27301) with the Nordic Optical Telescope (NOT) equipped with StanCAM, covering 100% of the afterglow region as provided by the Swift-XRT (Cenko et al. 27297). We obtained 3x300 s exposures with the Bessel R filter starting at 03:36:18 UT on March 3 (median time 1.161 hr after the GRB trigger) and 5x200 s exposures with the z-SDSS filter starting at 03:53:59 UT (median time 1.483 hr). We do not detect any optical afterglow candidate down to a limit of R > 23.0 mag (AB) and z > 21.5 mag (AB), calibrated against PS1 catalog. 
With the above upper limits, the optical to X-ray spectral index is then beta_OX < -0.09 (Fnu propto nu^-beta) computed assuming the R-Bessel value and X-rays data from Swift-XRT. This suggests a ‘’dark'' nature for GRB 200303A