GCN Circular 26573

W. C. Xue, Y. G. Zheng, C. Cai, Q. Luo, S. Xiao, Q. B. Yi, 
Y. Huang, C. K. Li, G. Li, X. B. Li, J. Y. Liao, S. L. Xiong,
C. Z. Liu, X. F. Li, Z. W. Li, Z. Chang, A. M. Zhang, 
Y. F. Zhang, X. F. Lu, C. L. Zou (IHEP), Y. J. Jin, 
Z. Zhang (THU), T. P. Li (IHEP/THU), F. J. Lu, L. M. Song, 
M. Wu, Y. P. Xu, S. N. Zhang (IHEP), 
report on behalf of the Insight-HXMT team:

At 2019-12-21T20:39:10.70 (T0), Insight-HXMT/HE detected 
GRB 191221B (trigger ID: HEB191221860) in a routine search of the data, 
which was also triggered by Swift/BAT (GCN #26534).

The Insight-HXMT/HE light curve mainly consists of multiple  
pulses with a duration (T90) of 8.85 s measured from T0-0.62 s. 
The 1-ms peak rate, measured from T0+5.37 s, is 8262 cnts/sec. 
The total counts from this burst is 38429 counts. 
URL_LC: http://www.hxmt.org/images/GRB/HEB191221860_LC.jpg

All measurements above are made with the CsI detectors operating in the 
regular mode with the energy range of about 80-800 keV (deposited energy). 
Only gamma-rays with energy greater than about 200 keV can penetrate 
the spacecraft and leave signals in the CsI detectors installed inside 
of the telescope. 

Insight-HXMT is the first Chinese space X-ray telescope, which was 
funded jointly by the China National Space Administration (CNSA) and 
the Chinese Academy of Sciences (CAS). 
More information about it could be found at: 
http://www.hxmt.org.