[vsnet-grb-info 27642] GRB 210402A: NOT optical upper limits

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  29745
SUBJECT: GRB 210402A: NOT optical upper limits
DATE:    21/04/03 02:55:03 GMT
FROM:    Dong Xu at NAOC/CAS  <dxu at nao.cas.cn>

Z.P. Zhu (NAOC, HUST), D. Xu (NAOC), L. Izzo (DARK/NBI), J. Martikainen 
(NOT) report on behalf of a larger collaboration:

We observed the field of GRB 210402A (Page et al., GCN 29743) using the 
Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. 
Observations started at 00:19:22 UT on 2021-04-03, i.e., 2.23 hr after 
the burst, and we obtained 3x300 s and 5x200 s frames in the SDSS r- and 
z- filters, respectively.

Preliminary analysis reveals that no optical transient is detected in 
our stacked images within or at the edge of the current XRT error circle 
(3.5 arcsec; Page et al., GCN 29743), down to limiting magnitudes of r ~ 
24.6 and z ~ 23.2, calibrated with nearby PanSTARRS stars.

Compared with the bright X-ray afterglow and no much X-ray column 
density excess, it may indicate that the burst is a high-redshift one.

NIR follow-ups are strongly encouraged.