[vsnet-grb-info 28251] GRB210702A: MeerLICHT multi-colour photometry

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  30354
SUBJECT: GRB210702A: MeerLICHT multi-colour photometry
DATE:    21/07/02 21:33:49 GMT
FROM:    Andrew Levan at U.of Leicester  <a.levan at astro.ru.nl>

P.J. Groot (Radboud/UCT/SAAO), S. de Wet (UCT), P.M. Vreeswijk
(Radboud), A.J. Levan (Radboud) report on behalf of the MeerLICHT
consortium:

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
calibration.

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.