[vsnet-grb-info 25234] GRB 200306C: Liverpool Telescope observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  27334
SUBJECT: GRB 200306C: Liverpool Telescope observations
DATE:    20/03/07 02:09:10 GMT
FROM:    Luca Izzo at DARK/NBI  <luca.izzo at gmail.com>

L. Izzo (DARK/NBI) and D. Perley (LJMU) report:

We observed GRB 200303A (Gropp et al. GCN 27326) with the IO:O camera mounted on the 2-m Liverpool Telescope located in La Palma, Spain. Observations started on March 7th at 01:01:49 UT (2.20 hours after the GRB trigger) and we obtained a series of 5x60s images in the griz filters.

In our stacked i-band and z-band images we detect the afterglow at the position reported by Swift-UVOT and other telescopes (Lipunov et al. GCNC 27324, GCN 27325; Jelinek et al. GCN 27328; Hu et al., GCN 27329; Moskvitin GCN 27333) and we measure a preliminary magnitude of i(AB) = 20.7 +- 0.1 mag (median time 2.46 hr after the GRB trigger) and z(AB) = 21.0 +- 0.3 mag (median time 2.58 hr after the GRB).  


> On 3 Mar 2020, at 16.25, Luca Izzo <luca.izzo at gmail.com> wrote:
> 
> 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