TITLE:   GCN CIRCULAR
NUMBER:  42189
SUBJECT: GRB 251009A: Insight-HXMT detection of a short burst
DATE:    25/10/10 16:17:00 GMT
FROM:    Chenwei Wang at IHEP <cwwang@ihep.ac.cn>

Chen-Wei Wang, Cheng-Kui Li, Shao-Lin Xiong, and Chao Zheng report on behalf of the Insight-HXMT team:

At 2025-10-09T15:58:56.350 (T0), Insight-HXMT/HE detected the burst GRB 251009A, which is also detected by Fermi/GBM (Fermi GBM team, GCN#42179) and SVOM/GRM (Wang et al., GCN#42185).

The Insight-HXMT/HE light curve mainly consists of a single pulse with a T90 of 0.65 +0.31/-0.28 s. The total counts from this burst is 998 counts.

The HXMT/HE light curve can be found here:
https://www.bursthub.cn//admin/static/hxmtgrb251009A.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.