TITLE:   GCN CIRCULAR
NUMBER:  41533
SUBJECT: GRB 250821B: Insight-HXMT detection
DATE:    25/08/25 03:30:20 GMT
FROM:    Chenwei Wang at IHEP <cwwang@ihep.ac.cn>

Chen-Wei Wang, Wen-Jun Tan, Shao-Lin Xiong, and Chao Zheng report on behalf of the Insight-HXMT team:

At 2025-08-21T16:07:47.500 (T0), Insight-HXMT/HE detected the bright intermedium duration burst GRB 250821B, which is also detected by Fermi/GBM (Fermi GBM team., GCN #41473), SVOM/GRM (Tan et al., GCN #41486) and Konus-Wind (D. Frederiks et al., GCN #41508).

The Insight-HXMT/HE light curve mainly consists of multi-pulses with a T90 of 2.05 +1.70/-0.45 s. The 1s peak rate, measured from T0-0.075 s, is 11927 cnts/sec. The total counts from this burst is 15817 counts.

The HXMT/HE light curve can be found here:
https://www.bursthub.cn//admin/static/hxmtgrb250821B.png

All measurements above are made with the CsI detectors operating in the regular mode with the energy range of about 60-900 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.