GRB 220712B
GCN Circular 32377
Subject
GRB 220712B: NOT optical afterglow confirmation
Date
2022-07-12T23:18:47Z (3 years ago)
From
Daniele B Malesani at Radboud U <d.malesani@astro.ru.nl>
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.