GCN Circular 32460

S. de Wet (UCT), P.J. Groot (Radboud/UCT/SAAO), D. Pieterse (Radboud), P.M.
Vreeswijk (Radboud), A.J. Levan (Radboud) and D.B. Malesani (Radboud and
DAWN/NBI) report on behalf of the MeerLICHT consortium:

Following the detection of GRB 220810A by Fermi/GBM (Fermi GBM team, GCN
32455
Not found
 
 
), the 0.6 m wide-field MeerLICHT optical telescope began a series of
automatically-triggered 60 s q-band exposures of a number of fields
encompassing the GBM error box. Observations began approximately 14 minutes
post-trigger at 23:30:01 UT on 2022 August 10, and continued for an hour.

A total of 20 fields encompassing a cumulative probability of 58% were
observed once each. Within our difference-imaging products for this dataset
we identify two new transient candidates with the following coordinates,
brightness, and observing times:

+---------------------------+-------------------------+----------------+------------------+----------+
| RA (J2000)                | Dec (J2000)             | Mag (AB)       |
5-sigma limiting | UT time  |
|                           |                         |                |
 mag (AB)        |          |
+---------------------------+-------------------------+----------------+------------------+----------+
| 20:45:15.77 (311.31569d)  | +05:06:39.95 (5.11110d) | 11.51 +/- 0.06 | q
> 15.79        | 23:59:19 |
+---------------------------+-------------------------+----------------+------------------+----------+
| 20:49:24.58 (312.35241d)  | +01:56:09.64 (1.93601d) | 17.52 +/- 0.07 | q
> 18.77        | 23:44:42 |
+---------------------------+-------------------------+----------------+------------------+----------+

These positions are calibrated against Gaia DR2 with a positional
uncertainty of 0.1" in each coordinate. We note that the first, bright
candidate was identified in an image in which the sources are trailed.
However, human inspection confirms that the source is not an artefact.

The position of both transients is within the 50% probability region of the
GBM error box, and no objects consistent with these positions and observing
times were found in the Minor Planet Centre database. We also note that no
underlying source is visible in archival PanSTARRS images at these
positions.

We obtained further observations of the second, fainter source on the
following night and obtained a 5-sigma limiting magnitude of q > 19.22 at
the transient position, consistent with fading behaviour. Further follow-up
observations are encouraged in order to determine if either of these
sources is the afterglow of GRB 220810A.

MeerLICHT is built and run by a consortium consisting of Radboud
University, the University of Cape Town, the South African Astronomical
Observatory, the University of Oxford, the University of Manchester and the
University of Amsterdam.