TITLE:   GCN CIRCULAR
NUMBER:  30837
SUBJECT: GRB 210912A: Tautenburg observations
DATE:    21/09/13 16:25:04 GMT
FROM:    Ana Nicuesa at TLS Tautenburg  <ana@tls-tautenburg.de>

A. Nicuesa Guelbenzu, S. Klose, S. Melnikov, B. Stecklum, C. Hoegner (all
TLS Tautenburg) report:

We observed the field of GRB 210912A (Troja et al., GCN 30820) with the
Tautenburg 1.34m Schmidt telescope equipped with the TAUKAM 6kx6k CCD
camera and the Sloan r-band filter.

Observations were performed on September 12, at a midtime of 19.33 UT,
22.17 UT, and 02:36 UT (Sep 13). The optical transient (Hu et al., GCN
30823; Pankov et al., GCN 30825; Kuin & Troja, GCN 30832; Kann et al. GCN
30833) is detected with the following preliminary AB magnitudes:

r_1 = 21.95 +- 0.19,
r_2 = 22.17 +- 0.19,
r_3 = 22.53 +- 0.19.

Magnitudes are calibrated against the Pan-STARRS catalogue.

A comparison with the previous observations suggests that around 0.6 days
the decay index of the light curve has increased from a rather modest
value of alpha = 0.4 to alpha about 1. Further observations are required
in order to provide a more precise decay index.