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GCN Circular 32377

GRB 220712B: NOT optical afterglow confirmation
2022-07-12T23:18:47Z (2 years ago)
Daniele B Malesani at Radboud U <>
D. B. Malesani (Radboud Univ. and DAWN/NBI), Z.P. Zhu (NAOC, HUST), M. 
A. Keniger (NOT), O. Durfeldt Pedros (NOT and DTU Space) report on 
behalf of a larger collaboration:

We observed again the field of GRB 220711B (D'Ai et al., GCN 32366) with 
the Nordic Optical Telescope equipped with the ALFOSC camera. 
Observations were carried out in the z band for a total of 25 min 
exposure. The mid time of the observation was 2022 Jul 12.92 UT (27.71 
hr after the GRB).

Object 1) identified by Malesani et al. (GCN 32368) has faded and is no 
longer detected in our images down to a limiting magnitude z > 23.5 AB 
(calibrated against nearby Pan-STARRS sources). We also note that the 
UVOT-enhanced XRT position (Beardmore et al., GCN 32370) has shifted and 
is fully consistent with the optical position.

We thus conclude that this object is the optical afterglow of GRB 220711B.

We note the red color of the afterglow: as measured in our images from 
last night (Malesani et al., GCN 32368), the afterglow had r-z > 2.2. As 
such, it is a potential high-redshift candidate (r dropout), though the 
large column density measured in the X-ray spectrum favors dust 
extinction as the explanation of the red color.
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