[vsnet-grb-info 20568] GRB 180418A: Further GROND observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  22666
SUBJECT: GRB 180418A: Further GROND observations
DATE:    18/04/20 14:14:21 GMT
FROM:    Patricia Schady at MPE/Swift  <pschady at mpe.mpg.de>

P. Schady and T.-W. Chen (both MPE Garching) report:

We re-observed the field of GRB 180418A (Swift trigger 826428; D'Elia et
al., GCN #22646) simultaneously in g'r'i'z'JHK with GROND (Greiner et al.
2008, PASP 120, 405) on 20th April, at a mid-time of 02UT. Observations
were performed at an average seeing of 1.2" and at an average airmass of
1.7.

Compared to the previous night of GROND observations (Schady, GCN #22662),
the target has decayed by ~0.8dex in the r'-band. Based on around 60
minutes of data, the estimated AB magnitudes from the second epoch of
GROND observations are:

g' = 24.5 +/- 0.2 mag
r' = 24.0 +/- 0.1 mag
i' = 23.4 +/- 0.2 mag
z' > 23.5 mag
J > 21.7 mag
H > 21.1 mag
K > 19.5 mag

Given magnitudes are calibrated against SDSS and 2MASS field stars, and
they are not corrected for the expected Galactic foreground extinction
corresponding to a reddening of E(B-V)=0.01 mag in the direction of the
burst (Schlafly & Finkbeiner 2011).

We thank Sam Kim for his excellent support from La Silla.