[vsnet-grb-info 20448] GRB 180325A: GROND observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  22544
SUBJECT: GRB 180325A: GROND observations
DATE:    18/03/25 17:51:03 GMT
FROM:    Alexander Kann at IAA-CSIC  <kann at iaa.es>

T. Schweyer (MPE), and D. A. Kann (HETH/IAA-CSIC) report:

We observed the field of GRB 180325A (Swift trigger 817564; E. Troja et 
al., GCN #22532) simultaneously in g'r'i'z'JHK with GROND (Greiner et 
al. 2008, PASP 120, 405) mounted at the 2.2 m MPG telescope at ESO La 
Silla Observatory (Chile).

Observations started at 02:53 UTC on March 25, 1.0 hours after the GRB 
trigger. They were performed at an average seeing of 1".5 and at an 
average airmass of 1.7.

We clearly detect the NIR/optical transient of GRB 180325A within the 
enhanced XRT position (J. P. Osborne et al., GCN #22539), in agreement 
with the optical transient detected by UVOT (E. Troja et al., GCN 
#22532).
Based on 7 minutes of exposure centered around 03:30 UTC, we measure the 
following magnitudes (all in AB system).

g' = 20.45 +/- 0.03 mag
r' = 19.57 +/- 0.02 mag
i' = 19.18 +/- 0.02 mag
z' = 18.30 +/- 0.02 mag
J = 17.42 +/- 0.02 mag
H = 16.85 +/- 0.02 mag
K = 16.34 +/ 0.03 mag

Given magnitudes are calibrated against SDSS in g'r'i'z' and 2MASS field 
stars in JHK, and are not corrected for the Galactic foreground 
extinction corresponding to a reddening of E_(B-V)= 0.015 in the
direction of the burst (Schlafly & Finkbeiner 2011).

We acknowledge the excellent support from the TiO and the current 
observer at the 2.2m in La Silla, Angela Hempel and Victor Marian.