TITLE:   GCN CIRCULAR
NUMBER:  29890
SUBJECT: GRB 210420B: continued Tautenburg observations
DATE:    21/04/23 10:03:42 GMT
FROM:    Sylvio Klose at TLS Tautenburg  <klose@tls-tautenburg.de>

A. Nicuesa Guelbenzu, S. Klose, S. Melnikov, B. Stecklum, and U. Laux (all 
Tautenburg) report:

We continued observing the afterglow of GRB 210420B (Moss et al., GCN 
29844) with the Tautenburg 1.34m Schmidt telescope equipped with the 
TAUKAM 6k x 6k CCD camera.

Results are:

- run 2: midtime 01:35 UT, April 22: r' = 21.40 +/- 0.20 mag
- run 3: midtime 23:24 UT, April 22: r' > 22.7  (3 sigma)

Magnitudes were calibrated against SDSS stars in the field.

Our data (see Stecklum et al., GCN 29863) imply that between the 2nd and 
the 3rd observing run the decay of the light curve has steepened from 
alpha = 0.99 +/- 0.04 to alpha = 2.3 +/- 0.9, with a break time at 1.14 
+/- 0.29 days. Probably this is the classical jet break time. No further 
observations are planned.