P.J. Groot (Radboud/UCT/SAAO), S. de Wet (UCT), P.M. Vreeswijk
(Radboud), A.J. Levan (Radboud) report on behalf of the MeerLICHT
Following the detection of GRB210702A by Swift and its optical
counterpart (Lien et al., GCN30351), the 0.6m MeerLICHT telescope,
located at Sutherland, South Africa obtained a series of 60s images in
the q,u,q,g,q,r,q,i,q,z,q,u,q,g,q bands, starting at 2021-07-02,
19:23:26.586 UT, 16 minutes after the Swift detection, and 3 minutes
after the distribution of the BAT alert.
The source identified by Swift UVOT is clearly detected as a new
transient at coordinates
RA(ICRS) = 168.57839 = 11:14:18.81 (+/-0.06���)
DEC(ICRS)= -36.74702 = -36:44:49.27 (+/- 0.04���)
MeerLICHT astrometry is calibrated against Gaia DR2.
The first source detections are, at:
q = 12.815 +/- 0.001 +/- 0.018 (19:23:26 UT)
u = 13.585 +/- 0.004 +/- 0.041 (19:25:10 UT)
g = 13.394 +/- 0.002 +/- 0.021 (19:28:46 UT)
r = 13.193 +/- 0.002 +/- 0.015 (19:32:18 UT)
i = 13.096 +/- 0.003 +/- 0.034 (19:35:42 UT)
z = 13.100 +/- 0.004 +/- 0.025 (19:39:25 UT)
where the first uncertainty on the magnitude is the statistical
uncertainty and the second is the uncertainty on the photometric
Our repeated q-band observations show decay consistent with a power law
with exponent of approximately -1.2.
Further data taking was suspended due to high winds.
Reference images of the field show no underlying host galaxy down to
the 5-sigma limiting magnitude, at the position of the afterglow, at:
u > 19.54
g > 20.44
q > 21.23
r > 20.20
i > 19.72
z > 18.90
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.