TITLE:   GCN CIRCULAR
NUMBER:  31401
SUBJECT: GRB 220101A: Tautenburg observations
DATE:    22/01/07 18:12:34 GMT
FROM:    Sylvio Klose at TLS Tautenburg  <klose@tls-tautenburg.de>

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

We continued observing the field of GRB 220101A (Tohuvavohu et al., GCN 
31347) with the Tautenburg 1.34m Schmidt telescope equipped with the 
TAUKAM 6kx6k CCD camera (Stecklum et al. 2021; arXiv:2101.12554).

For the optical transient (discovered by Swift/UVOT: Tohuvavohu et al., 
GCN 31347; Kuin et al., GCN 31351) we measure the following AB magnitudes:

g > 22.9  (3 sigma), January 6, 20:23 UT (midtime),
r = 22.54 +/- 0.24,  January 6, 19:32 UT (midtime),
i = 21.27 +/- 0.10,  January 6, 18:44 UT (midtime),
z = 21.17 +/- 0.22,  January 6, 18:26 UT (midtime),

calibrated against the SDSS catalogue.