GCN Circular 30695
Subject
GRB 210820A: GROND observations
Event
Date
2021-08-23T13:50:31Z (5 years ago)
From
Ana Nicuesa at TLS Tautenburg <ana@tls-tautenburg.de>
A. Nicuesa Guelbenzu, S. Klose (both TLS Tautenburg) and
A. Rau (MPE Garching) report:
We observed the field of GRB 210820A (Swift trigger 1069551); Beardmore et
al., GCN 30664) simultaneously in g'r'i'z'JHK with GROND mounted at the
2.2 m MPG/ESO telescope at La Silla Observatory (Chile).
Observations were performed at 9:03 UT (midtime) on August 21, 2021,
about 15.5 hours after the GRB trigger. They were executed at an
average seeing of 1.3 arcsec and at an average airmass of 1.2.
We detect a source within the XRT error circle (Beardmore, et al.,
GCN 30667) in the i' band with the following preliminary AB
magnitude
i'=22.46 +/- 0.28
in agreement with the RATIR detection (Butler et al., GCN 30672).
We do not detect the source in the other bands down to the following
limiting AB magnitudes:
g' > 22.6,
r' > 22.9,
z' > 22.3,
J > 20.9,
H > 20.4, and
K > 17.4.
The given limits and magnitude are derived based on calibrating the images
against SDSS in g'r'i'z' and 2MASS field stars in JHK.
We thank Paul Eigenthaler for excellent support and for performing the
observations.