TITLE:   GCN CIRCULAR
NUMBER:  27571
SUBJECT: GRB 200412B:  Xinglong TNT  optical observations
DATE:    20/04/14 04:22:19 GMT
FROM:    Liping Xin at NAOC, SVOM  <xlp@nao.cas.cn>

L. P. Xin, X. F. Wang,  J. Zheng, Y. L. Qiu, J. Y. Wei,  J. Wang,  
L. H. Li ,  C. Wu,  X. H. Han and J. S. Deng, report:

We began to observe GRB 200412B (The Fermi GBM team,
GCN 27547; Longo et al. GCN 27557)  
with Xinglong TNT telescope at 18:09:54 (UT), 13th. Apr. 2020,  
about 33 hours after  the burst. 

10  x 300 sec R band images were obtained. 

The optical afterglow  (Lipunov et al., GCNs 27555, 27556; Kumar et al., GCN
27564; Belkin et al., GCN 27566, Stecklum et al., GCN 27567, 
Moskvitin GCN 27570) is clearly detected in individual
images with the brightness of R = 20.0 +/- 0.1.
The photometry is based on R2 magnitudes of nearby USNO-B1 stars.

With the reports from  (Kumar et al., GCN
27564; Belkin et al., GCN 27566, Stecklum et al., GCN 27567, 
Moskvitin GCN 27570), the brightness is fading with a slope of  -1.5 
for a single power law (t~t^a) from 10 hours to 39 hours after the burst trigger.