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GCN Circular 32281

Subject
GRB 220627A: MeerLICHT detection of two afterglow candidates
Date
2022-06-28T02:12:29Z (2 years ago)
From
Paul Groot at Radboud University Nijmegen <p.groot@astro.ru.nl>
P.J. Groot (Radboud/UCT/SAAO), S. de Wet (UCT/SAAO), P.M. Vreeswijk
(Radboud) report on behalf of the MeerLICHT consortium:

Following the detection of GRB220627A by Fermi (Fermi GBM team, GCN
32278) the MeerLICHT 0.6m wide-field optical telescope, located at
SAAO Sutherland, South Africa, started scanning the error box at
2022-06-27 21:43 UT (T0+23 minutes and 3 minutes after the alert was
received). Observations were obtained in the q-band (440-720nm), using
52 tiles (146 square degrees) to cover a 71% cumulative
probabilty. Before the observability limit of HA=+4.5 hr was reached
32.4 square degrees were covered at least twice, covering a cumulative
probability of 7.5% of the Fermi error box.

Automatic data processing using BlackBOX/ZOGY resulted in 7 new
transients that were observed at least twice and were detected with a
significance >12 in the difference images. Five of these candidates
can be associated to known asteroids. 

The remaining two candidates are uncataloged and are both detected
three times: 

Candidate 1 is MLTJ143615.50-360417.3,
at RA,Dec (ICRS) 14:36:15.50, -36:04:17.3 (219.06459,-36.07149),
first detected at q_AB = 18.13+/-0.03 on 2022-06-27 22:50:22/05 (MJD
59757.95164). Last non-detection was on MJD 58971.02.19 at q_AB > 20.35
(for a transient source).  

Candidate 2 is MLTJ143614.90-373629.0,
at RA,Dec (ICRS) 14:36:14.90. -37:36:29.0 (219.06217,-37.60809),
first detected at q_AB = 19.62+/-0.10, on 2022-06-27 22:53:20.54 (MJD
59757.95371). Last non-detection was on MJD 59737.8835 at q_AB > 20.82

Candidate 1 shows the presence of an underlying object in the MeerLICHT
reference image at q_AB = 20.72, possibly a host galaxy. 
Candidate 2 shows no underlying source in the MeerLICHT reference image
with a limiting magnitude of q_AB > 20.28. 

During the three MeerLICHT observations Candidate 1 evolved to q_AB =
18.21 +/-0.02 at 2022-06-27 23:16:51 (MJD 59757.97004). Candidate 2
brightened to q_AB = 19.43 +/- 0.10 at 2022-06-27 23:18:14 (MJD
59757.97100).

Follow-up observations of both candidates are encouraged. 

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